ANALOG DEVICES AD7858

3 V to 5 V Single Supply, 200 kSPS a 8-Channel, 12-Bit Sampling ADC AD7858/AD7858L FUNCTIONAL BLOCK DIAGRAM FEATURES Specified for V of 3 V to 5.5 V DD AD7858—200 kSPS; AD7858L—100 kSPS AV DD AGND System and Self-Calibration with Autocalibration on Power-Up AIN1 AD7858/ Eight Single-Ended or Four Pseudo-Differential Inputs I/P T/H AD7858L MUX Low Power DV DD AIN8 AD7858: 12 mW (V = 3 V) DD 2.5V AD7858L: 4.5 mW (V = 3 V) REFERENCE DD COMP Automatic Power-Down After Conversion (25�W) Flexible Serial Interface: DGND REF /REF BUF IN OUT 8051/SPI™/QSPI™/�P Compatible C 24-Lead DIP, SOIC, and SSOP Packages REF1 CHARGE APPLICATIONS REDISTRIBUTION DAC Battery-Powered Systems (Personal Digital Assistants, CLKIN Medical Instruments, Mobile Communications) C REF2 CONVST SAR AND ADC Pen Computers CONTROL CALIBRATION BUSY Instrumentation and Control Systems MEMORY AND CAL CONTROLLER SLEEP High-Speed Modems GENERAL DESCRIPTION SERIAL INTERFACE/CONTROL REGISTER The AD7858/AD7858L are high-speed, low-power, 12-bit ADCs that operate from a single 3 V or 5 V power supply, the DIN DOUT SCLK SYNC AD7858 being optimized for speed and the AD7858L for low power. The ADC powers up with a set of default conditions at which time it can be operated as a read-only ADC. The ADC PRODUCT HIGHLIGHTS contains self-calibration and system calibration options to en- 1. Specified for 3 V and 5 V supplies. sure accurate operation over time and temperature and have a number of power-down options for low-power applications. 2. Automatic calibration on power-up. The part powers up with a set of default conditions and can 3. Flexible power management options including automatic operate as a read-only ADC. power-down after conversion. The AD7858 is capable of 200 kHz throughput rate while the 4. Operates with reference voltages from 1.2 V to V . DD AD7858L is capable of 100 kHz throughput rate. The input 5. Analog input range from 0 V to V . DD track-and-hold acquires a signal in 500 ns and features a pseudo-differential sampling scheme. The AD7858/AD7858L 6. Eight single-ended or four pseudo-differential input channels. voltage range is 0 to V with straight binary output coding. REF 7. System and self-calibration. Input signal range is to the supply and the part is capable of con- 8. Versatile serial I/O port (SPI/QSPI/8051/µP). verting full power signals to 100 kHz. 9. Lower power version AD7858L. CMOS construction ensures low power dissipation of typically 4.5 mW for normal operation and 1.15 mW in power-down mode with a throughput rate of 10 kSPS (V = 3 V). The part DD is available in 24-lead, 0.3 inch-wide dual-in-line package (DIP), 24-lead small outline (SOIC), and 24-lead small shrink outline (SSOP) packages. See page 31 for data sheet index. SPI and QSPI are trademarks of Motorola, Inc. REV. B Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. use, nor for any infringements of patents or other rights of third parties Tel: 781/329-4700 World Wide Web Site: http://www.analog.com which may result from its use. No license is granted by implication or Fax: 781/326-8703 © Analog Devices, Inc., 2000 otherwise under any patent or patent rights of Analog Devices. 1, 2 AD7858/AD7858L–SPECIFICATIONS (AV = DV = +3.0 V to +5.5 V, REF /REF = 2.5 V External DD DD IN OUT Reference unless otherwise noted, f = 4 MHz (1.8 MHz B Grade (0�C to +70�C), 1 MHz A and B Grades (–40�C to +85�C) for L Version); f = CLKIN SAMPLE 200 kHz (AD7858), 100 kHz (AD7858L); SLEEP = Logic High; T = T to T , unless otherwise noted.) Specifications in ( ) apply to the AD7858L. A MIN MAX 1 1 Parameter A Version B Version Units Test Conditions/Comments DYNAMIC PERFORMANCE 3 Signal to Noise + Distortion Ratio 70 71 dB min Typically SNR is 72 dB (SNR) V = 10 kHz Sine Wave, f = 200 kHz (100 kHz) IN SAMPLE Total Harmonic Distortion (THD) –78 –78 dB max V = 10 kHz Sine Wave, f = 200 kHz (100 kHz) IN SAMPLE Peak Harmonic or Spurious Noise –78 –78 dB max V = 10 kHz Sine Wave, f = 200 kHz (100 kHz) IN SAMPLE Intermodulation Distortion (IMD) Second Order Terms –78 –80 dB typ fa = 9.983 kHz, fb = 10.05 kHz, f = 200 kHz (100 kHz) SAMPLE Third Order Terms –78 –80 dB typ fa = 9.983 kHz, fb = 10.05 kHz, f = 200 kHz (100 kHz) SAMPLE Channel-to-Channel Isolation –90 –90 dB typ V = 25 kHz IN DC ACCURACY Any Channel Resolution 12 12 Bits Integral Nonlinearity ±1 ±1 LSB max 2.5 V External Reference V = 3 V, V = 5 V (B Grade Only) DD DD ±1 ±0.5 LSB max 5 V External Reference V = 5 V DD (±1) LSB max (L Version, 5 V External Reference, V = 5 V) DD (±1) LSB max (L Version) Differential Nonlinearity ±1 ±1 LSB max Guaranteed No Missed Codes to 12 Bits. 2.5 V External Reference V = 3 V, 5 V External Reference, V = 5 V DD DD Total Unadjusted Error ±1 ±1 LSB typ Unipolar Offset Error ±5 ±5 LSB max Typically ±2 LSBs ±2.5 ±2.5 LSB max 5 V External Reference, V = 5 V DD (±3) (±3) LSB max (L Version) (±1.5) (±1.5) LSB max (L Version, 5 V External Reference, V = 5 V) DD Unipolar Offset Error Match 1.5 1.5 LSB max Positive Full-Scale Error ±4 ±4 LSB max ±1.5 ±1.5 LSB max 5 V External Reference, V = 5 V DD Positive Full-Scale Error Match 1 1 LSB max ANALOG INPUT Input Voltage Ranges 0 to V 0 to V Volts i.e., AIN(+) – AIN(–) = 0 to V , AIN(–) can be biased REF REF REF up but AIN(+) cannot go below AIN(–) Leakage Current ±1 ±1 µA max Input Capacitance 20 20 pF typ REFERENCE INPUT/OUTPUT REF Input Voltage Range 2.3/V 2.3/V V min/max Functional from 1.2 V IN DD DD Input Impedance 150 150 kΩ typ REF Output Voltage 2.3/2.7 2.3/2.7 V min/max OUT REF Tempco 20 20 ppm/°C typ OUT LOGIC INPUTS Input High Voltage, V 2.4 2.4 V min AV = DV = 4.5 V to 5.5 V INH DD DD 2.1 2.1 V min AV = DV = 3.0 V to 3.6 V DD DD Input Low Voltage, V 0.8 0.8 V max AV = DV = 4.5 V to 5.5 V INL DD DD 0.6 0.6 V max AV = DV = 3.0 V to 3.6 V DD DD Input Current, I ±10 ±10 µA max Typically 10 nA, V = 0 V or V IN IN DD 4 Input Capacitance, C 10 10 pF max IN LOGIC OUTPUTS Output High Voltage, V I = 200 µA OH SOURCE 4 4 V min AV = DV = 4.5 V to 5.5 V DD DD 2.4 2.4 V min AV = DV = 3.0 V to 3.6 V DD DD Output Low Voltage, V 0.4 0.4 V max I = 0.8 mA OL SINK Floating-State Leakage Current ±10 ±10 µA max 4 Floating-State Output Capacitance 10 10 pF max Output Coding Straight (Natural) Binary CONVERSION RATE Conversion Time 4.6 (18) 4.6 µs max (L Versions Only, –40°C to +85°C, 1 MHz CLKIN) (10) µs max (L Versions Only, 0°C to +70°C, 1.8 MHz CLKIN) Track/Hold Acquisition Time 0.4 (1) 0.4 (1) µs min (L Versions Only) –2– REV. B AD7858/AD7858L 1 1 Parameter A Version B Version Units Test Conditions/Comments DYNAMIC PERFORMANCE AV DV +3.0/+5.5 +3.0/+5.5 V min/max DD, DD I DD 5 Normal Mode 6 (1.9) 6 (1.9) mA max AV = DV = 4.5 V to 5.5 V. Typically 4.5 mA (1.5) DD DD 5.5 (1.9) 5.5 (1.9) mA max AV = DV = 3.0 V to 3.6 V. Typically 4.0 mA (1.5 mA) DD DD 6 Sleep Mode With External Clock On 10 10 µA typ Full Power-Down. Power Management Bits in Control Register Set as PMGT1 = 1, PMGT0 = 0 400 400 µA typ Partial Power-Down. Power Management Bits in Control Register Set as PMGT1 = 1, PMGT0 = 1 With External Clock Off 5 5 µA max Typically 1 µA. Full Power-Down. Power Management Bits in Control Register Set as PMGT1 = 1, PMGT0 = 0 200 200 µA typ Partial Power-Down. Power Management Bits in Control Register Set as PMGT1 = 1, PMGT0 = 1 Normal-Mode Power Dissipation 33 (10.5) 33 (10.5) mW max V = 5.5 V. Typically 25 mW (8); SLEEP = V DD DD 20 (6.85) 20 (6.85) mW max V = 3.6 V. Typically 15 mW (5.4); SLEEP = V DD DD Sleep Mode Power Dissipation With External Clock On 55 55 µW typ V = 5.5 V. SLEEP = 0 V DD 36 36 µW typ V = 3.6 V. SLEEP = 0 V DD With External Clock Off 27.5 27.5 µW max V = 5.5 V. Typically 5.5 µW; SLEEP = 0 V DD 18 18 µW max V = 3.6 V. Typically 3.6 µW; SLEEP = 0 V DD SYSTEM CALIBRATION 7 Offset Calibration Span +0.05 × V /–0.05 × V V max/min Allowable Offset Voltage Span for Calibration REF REF 7 Gain Calibration Span +1.025 × V /–0.975 × V V max/min Allowable Full-Scale Voltage Span for Calibration REF REF NOTES 1 Temperature ranges as follows: A, B Versions: –40°C to +85°C. For L Versions, A and B Versions f = 1 MHz over –40°C to +85°C temperature range, CLKIN B Version f = 1.8 MHz over 0°C to +70°C temperature range. CLKIN 2 Specifications apply after calibration. 3 SNR calculation includes distortion and noise components. 4 Sample tested @ +25°C to ensure compliance. 5 All digital inputs @ DGND except for CONVST, SLEEP, CAL, and SYNC @ DV . No load on the digital outputs. Analog inputs @ AGND. DD 6 CLKIN @ DGND when external clock off. All digital inputs @ DGND except for CONVST, SLEEP, CAL, and SYNC @ DV . No load on the digital DD outputs. Analog inputs @ AGND. 7 The Offset and Gain Calibration Spans are defined as the range of offset and gain errors that the AD7858/AD7858L can calibrate. Note also that these are voltage spans and are not absolute voltages ( i.e., the allowable system offset voltage presented at AIN(+) for the system offset error to be adjusted out will be AIN(–) ±0.05 × V , and the allowable system full-scale voltage applied between AIN(+) and AIN(–) for the system full-scale voltage error to be adjusted out will be REF V ± 0.025 × V ). This is explained in more detail in the Calibration section of the data sheet. REF REF Specifications subject to change without notice. REV. B –3– AD7858/AD7858L (AV = DV = +3.0 V to +5.5 V; f = 4 MHz for AD7858 and 1.8/1 MHz for AD7858L; DD DD CLKIN 1 T = T to T , unless otherwise noted) TIMING SPECIFICATIONS A MIN MAX Limit at T , T MIN MAX (A, B Versions) Parameter 5 V 3 V Units Description 2 f 500 500 kHz min Master Clock Frequency CLKIN 4 4 MHz max 1.8 1.8 MHz max L Version, 0°C to +70°C, B Grade Only 1 1 MHz max L Version, –40°C to +85°C f 4 4 MHz max SCLK 3 t 100 100 ns min CONVST Pulsewidth 1 t 50 90 ns max CONVST↓ to BUSY↑ Propagation Delay 2 t 4.6 4.6 µs max Conversion Time = 18 t CONVERT CLKIN 10 (18) 10 (18) µs max L Version 1.8 (1) MHz CLKIN. Conversion Time = 18 t CLKIN t –0.4 t –0.4 t ns min SYNC↓ to SCLK↓ Setup Time (Noncontinuous SCLK Input) 3 SCLK SCLK �0.4 t �0.4 t ns min/max SYNC↓ to SCLK↓ Setup Time (Continuous SCLK Input) SCLK SCLK 4 t 50 90 ns max Delay from SYNC↓ Until DOUT Three-State Disabled 4 4 t 50 90 ns max Delay from SYNC↓ Until DIN Three-State Disabled 5 4 t 75 115 ns max Data Access Time After SCLK↓ 6 t 40 60 ns min Data Setup Time Prior to SCLK↑ 7 t 20 30 ns min Data Valid to SCLK Hold Time 8 t 0.4 t 0.4 t ns min SCLK High Pulsewidth 9 SCLK SCLK t 0.4 t 0.4 t ns min SCLK Low Pulsewidth 10 SCLK SCLK t 30 50 ns min SCLK↑ to SYNC↑ Hold Time (Noncontinuous SCLK) 11 30/0.4 t 50/0.4 t ns min/max (Continuous SCLK) SCLK SCLK 5 t 50 50 ns max Delay from SYNC↑ Until DOUT Three-State Enabled 12 t 90 130 ns max Delay from SCLK↑ to DIN Being Configured as Output 13 6 t 50 90 ns max Delay from SCLK↑ to DIN Being Configured as Input 14 t 2.5 t 2.5 t ns max CAL↑ to BUSY↑ Delay 15 CLKIN CLKIN t 2.5 t 2.5 t ns max CONVST↓ to BUSY↑ Delay in Calibration Sequence 16 CLKIN CLKIN 7 t 31.25 31.25 ms typ Full Self-Calibration Time, Master Clock Dependent CAL (125013 t ) CLKIN 7 t 27.78 27.78 ms typ Internal DAC Plus System Full-Scale Calibration Time, Master CAL1 Clock Dependent (111114 t ) CLKIN 7 t 3.47 3.47 ms typ System Offset Calibration Time, Master Clock Dependent CAL2 (13899 t ) CLKIN NOTES 1 Sample tested at +25°C to ensure compliance. All input signals are specified with tr = tf = 5 ns (10% to 90% of V ) and timed from a voltage level of 1.6 V. DD See Table XI and timing diagrams for different interface modes and Calibration. 2 Mark/Space ratio for the master clock input is 40/60 to 60/40. 3 The CONVST pulsewidth will apply here only for normal operation. When the part is in power-down mode, a different CONVST pulsewidth will apply (see Power-Down section). 4 Measured with the load circuit of Figure 1 and defined as the time required for the output to cross 0.8 V or 2.4 V. 5 t is derived form the measured time taken by the data outputs to change 0.5 V when loaded with the circuit of Figure 1. The measured number is then extrapolated 12 back to remove the effects of charging or discharging the 100 pF capacitor. This means that the time, t , quoted in the timing characteristics is the true bus 12 relinquish time of the part and is independent of the bus loading. 6 t is derived form the measured time taken by the data outputs to change 0.5 V when loaded with the circuit of Figure 1. The measured number is then 14 extrapolated back to remove the effects of charging or discharging the 100 pF capacitor. This means that the time quoted in the Timing Characteristics is the true delay of the part in turning off the output drivers and configuring the DIN line as an input. Once this time has elapsed the user can drive the DIN line knowing that a bus conflict will not occur. 7 The typical time specified for the calibration times is for a master clock of 4 MHz. For the L version the calibration times will be longer than those quoted here due to the 1.8/1 MHz master clock. Specifications subject to change without notice. –4– REV. B AD7858/AD7858L TYPICAL TIMING DIAGRAMS 1.6mA I Figures 2 and 3 show typical read and write timing diagrams for OL serial Interface Mode 2. The reading and writing occurs after TO conversion in Figure 2, and during conversion in Figure 3. To +2.1V OUTPUT attain the maximum sample rate of 100 kHz (AD7858L) or C PIN L 100pF 200 kHz (AD7858), reading and writing must be performed during conversion as in Figure 3. At least 400 ns acquisition 200�A I OH time must be allowed (the time from the falling edge of BUSY to the next rising edge of CONVST) before the next conversion Figure 1. Load Circuit for Digital Output Timing begins to ensure that the part is settled to the 12-bit level. If the Specifications user does not want to provide the CONVST signal, the conver- sion can be initiated in software by writing to the control register. t = 4.6�s MAX, 10�s MAX FOR L VERSION CONVERT t = 100ns MIN, t = 50/90ns MAX 5V/3V, t = 40/60ns MIN 5V/3V 1 4 7 t 1 CONVST (I/P) t CONVERT t 2 BUSY (O/P) SYNC (I/P) t t 3 t 9 11 15616 SCLK (I/P) t t 4 10 t 12 t t 6 6 THREE-STATE THREE- DOUT (O/P) DB15 DB11 DB0 STATE t 8 t 7 DIN (I/P) DB15 DB11 DB0 Figure 2. AD7858/AD7858L Timing Diagram for Interface Mode 2 (Reading/Writing After Conversion) t = 4.6�s MAX, 10�s MAX FOR L VERSION CONVERT t = 100ns MIN, t = 50/90ns MAX 5V/3V, t = 40/60ns MIN 5V/3V 1 4 7 t 1 CONVST (I/P) t CONVERT t 2 BUSY (O/P) SYNC (I/P) t t t 3 11 9 15616 SCLK (I/P) t t 4 10 t 12 t t 6 6 THREE-STATE THREE- DOUT (O/P) DB15 DB11 DB0 STATE t 8 t 7 DIN (I/P) DB15 DB11 DB0 Figure 3. AD7858/AD7858L Timing Diagram for Interface Mode 2 (Reading/Writing During Conversion) REV. B –5– AD7858/AD7858L 1 ABSOLUTE MAXIMUM RATINGS SOIC, SSOP Package, Power Dissipation . . . . . . . . . . 450 mW (T = +25°C unless otherwise noted) θ Thermal Impedance . . . 75°C/W (SOIC) 115°C/W (SSOP) A JA θ Thermal Impedance . . . . 25°C/W (SOIC) 35°C/W (SSOP) JC AV to AGND . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V DD Lead Temperature, Soldering DV to DGND . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V DD Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . +215°C AV to DV . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +0.3 V DD DD Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . +220°C Analog Input Voltage to AGND . . . . –0.3 V to AV + 0.3 V DD NOTES Digital Input Voltage to DGND . . . . –0.3 V to DV + 0.3 V DD 1 Stresses above those listed under Absolute Maximum Ratings may cause perma- Digital Output Voltage to DGND . . . –0.3 V to DV + 0.3 V DD nent damage to the device. This is a stress rating only; functional operation of the REF /REF to AGND . . . . . . . . . –0.3 V to AV + 0.3 V IN OUT DD device at these or any other conditions above those listed in the operational 2 Input Current to Any Pin Except Supplies . . . . . . . ±10 mA sections of this specification is not implied. Exposure to absolute maximum rating Operating Temperature Range conditions for extended periods may affect device reliability. 2 Transient currents of up to 100 mA will not cause SCR latch-up. Commercial (A, B Versions) . . . . . . . . . . . –40°C to +85°C Storage Temperature Range . . . . . . . . . . . –65°C to +150°C Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . +150°C Plastic DIP Package, Power Dissipation . . . . . . . . . . 450 mW θ Thermal Impedance . . . . . . . . . . . . . . . . . . . . . 105°C/W JA θ Thermal Impedance . . . . . . . . . . . . . . . . . . . . 34.7°C/W JC Lead Temperature, (Soldering, 10 sec) . . . . . . . . . . +260°C CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily WARNING! accumulate on the human body and test equipment and can discharge without detection. Although the AD7858/AD7858L features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions ESD SENSITIVE DEVICE are recommended to avoid performance degradation or loss of functionality. PIN CONFIGURATIONS ORDERING GUIDE DIP, SOIC, AND SSOP Linearity Power Error Dissipation Package 1 2 Model (LSB) (mW) Options 1 24 CONVST SYNC BUSY 2 23 SCLK AD7858AN ±1 20 N-24 3 22 SLEEP CLKIN AD7858BN ±1/2 20 N-24 REF /REF 3 4 21 DIN IN OUT AD7858LAN ±1 6.85 N-24 AD7858/ AV 5 3 DD 20 DOUT AD7858L AD7858LBN ±1 6.85 N-24 AGND 6 19 DGND TOP VIEW AD7858AR ±1 20 R-24 (Not to Scale) C 7 18 DV REF1 DD AD7858BR ±1/2 20 R-24 C 3 8 17 CAL REF2 AD7858LAR ±1 6.85 R-24 AIN1 AIN8 3 9 16 AD7858LBR ±1 6.85 R-24 10 3 AIN2 15 AIN7 AD7858LARS ±1 6.85 RS-24 AIN3 AIN6 4 11 14 EVAL-AD7858CB AIN4 12 5 13 AIN5 EVAL-CONTROL BOARD NOTES 1 Linearity error here refers to integral linearity error. 2 N = Plastic DIP; R = SOIC; RS = SSOP. 3 L signifies the low-power version. 4 This can be used as a stand-alone evaluation board or in conjunction with the EVAL- CONTROL BOARD for evaluation/demonstration purposes. 5 This board is a complete unit allowing a PC to control and communicate with all Analog Devices evaluation boards ending in the CB designators. –6– REV. B AD7858/AD7858L PIN FUNCTION DESCRIPTIONS Pin Mnemonic Description 1 CONVST Convert Start. Logic Input. A low to high transition on this input puts the track/hold into its hold mode and starts conversion. When this input is not used, it should be tied to DV . DD 2 BUSY Busy Output. The busy output is triggered high by the falling edge of CONVST or rising edge of CAL, and remains high until conversion is completed. BUSY is also used to indicate when the AD7858/ AD7858L has completed its on-chip calibration sequence. 3 SLEEP Sleep Input/Low-Power Mode. A Logic 0 initiates a sleep, and all circuitry is powered down including the internal voltage reference provided there is no conversion or calibration being performed. Calibration data is retained. A Logic 1 results in normal operation. See Power-Down section for more details. 4 REF /REF Reference Input/Output. This pin is connected to the internal reference through a series resistor and is IN OUT the reference source for the analog-to-digital converter. The nominal reference voltage is 2.5 V and this appears at the pin. This pin can be overdriven by an external reference or can be taken as high as AV . DD When this pin is tied to AV or when an externally applied reference approaches AV , the C pin DD, DD REF1 should also be tied to AV . DD 5AV Analog Positive Supply Voltage, +3.0 V to +5.5 V. DD 6 AGND Analog Ground. Ground reference for track/hold, reference, and DAC. 7C Reference Capacitor (0.1 µF Multilayer Ceramic). This external capacitor is used as a charge source for REF1 the internal DAC. The capacitor should be tied between the pin and AGND. 8C Reference Capacitor (0.01 µF Ceramic Disc). This external capacitor is used in conjunction with the on- REF2 chip reference. The capacitor should be tied between the pin and AGND. 9–16 AIN1–AIN8 Analog Inputs. Eight analog inputs that can be used as eight single-ended inputs (referenced to AGND) or four pseudo-differential inputs. Channel configuration is selected by writing to the control register. Both the positive and negative inputs cannot go below AGND or above AV at any time. Also the posi- DD tive input cannot go below the negative input. See Table III for channel selection. 17 CAL Calibration Input. This pin has an internal pull-up current source of 0.15 µA. A Logic 0 on this pin resets all calibration control logic and initiates a calibration on its rising edge. There is the option of connecting a 10 nF capacitor from this pin to DGND to allow for an automatic self-calibration on power-up. This input overrides all other internal operations. If the autocalibration is not required, this pin should be tied to a logic high. 18 DV Digital Supply Voltage, +3.0 V to +5.5 V. DD 19 DGND Digital Ground. Ground reference point for digital circuitry. 20 DOUT Serial Data Output. The data output is supplied to this pin as a 16-bit serial word. 21 DIN Serial Data Input. The data to be written is applied to this pin in serial form (16-bit word). This pin can act as an input pin or as a I/O pin depending on the serial interface mode the part is in (see Table X). 22 CLKIN Master clock signal for the device (4 MHz AD7858, 1.8 MHz AD7858L). Sets the conversion and cali- bration times. 23 SCLK Serial Port Clock. Logic Input. The user must provide a serial clock on this input. 24 SYNC Frame Sync. Logic Input. This pin is level triggered active low and frames the serial clock for the read and write operations (see Table IX). REV. B –7– AD7858/AD7858L 1 Total Harmonic Distortion TERMINOLOGY Total harmonic distortion (THD) is the ratio of the rms sum of Integral Nonlinearity harmonics to the fundamental. For the AD7858/AD7858L, it is This is the maximum deviation from a straight line passing defined as: through the endpoints of the ADC transfer function. The end- points of the transfer function are zero scale, a point 1/2 LSB 2 2 2 2 2 below the first code transition, and full scale, a point 1/2 LSB (V + V + V + V + V ) 2 3 4 5 6 THD dB = 20 log () above the last code transition. V 1 Differential Nonlinearity where V is the rms amplitude of the fundamental and V , V , 1 2 3 This is the difference between the measured and the ideal 1 LSB V , V , and V are the rms amplitudes of the second through the 4 5 6 change between any two adjacent codes in the ADC. sixth harmonics. Total Unadjusted Error Peak Harmonic or Spurious Noise This is the deviation of the actual code from the ideal code tak- Peak harmonic or spurious noise is defined as the ratio of the ing all errors into account (Gain, Offset, Integral Nonlinearity, and rms value of the next largest component in the ADC output other errors) at any point along the transfer function. spectrum (up to f /2 and excluding dc) to the rms value of the S Unipolar Offset Error fundamental. Normally, the value of this specification is deter- This is the deviation of the first code transition (00 . . . 000 to mined by the largest harmonic in the spectrum, but for parts 00 . . . 001) from the ideal AIN(+) voltage (AIN(–) + 1/2 LSB). where the harmonics are buried in the noise floor, it will be a noise peak. Positive Full-Scale Error This is the deviation of the last code transition from the ideal Intermodulation Distortion AIN(+) voltage (AIN(–) + Full Scale – 1.5 LSB) after the offset With inputs consisting of sine waves at two frequencies, fa and error has been adjusted out. fb, any active device with nonlinearities will create distortion products at sum and difference frequencies of mfa ± nfb where Channel-to-Channel Isolation m, n = 0, 1, 2, 3, etc. Intermodulation distortion terms are Channel-to-channel isolation is a measure of crosstalk between those for which neither m nor n are equal to zero. For example, the channels. It is measured by applying a full-scale 25 kHz the second order terms include (fa + fb) and (fa – fb), while the signal to the other seven channels and determining how much third order terms include (2fa + fb), (2fa – fb), (fa + 2fb), and that signal is attenuated in the channel of interest. The figure (fa – 2fb). given is the worst case for all channels. Testing is performed using the CCIF standard where two input Track/Hold Acquisition Time frequencies near the top end of the input bandwidth are used. In The track/hold amplifier returns into track mode and the end of this case, the second order terms are usually distanced in fre- conversion. Track/hold acquisition time is the time required for quency from the original sine waves, while the third order terms the output of the track/hold amplifier to reach its final value, are usually at a frequency close to the input frequencies. As a within ±1/2 LSB, after the end of conversion. result, the second and third order terms are specified separately. Signal to (Noise + Distortion) Ratio The calculation of the intermodulation distortion is as per the This is the measured ratio of signal to (noise + distortion) at the THD specification where it is the ratio of the rms sum of the output of the A/D converter. The signal is the rms amplitude of individual distortion products to the rms amplitude of the sum the fundamental. Noise is the sum of all nonfundamental signals of the fundamentals expressed in dBs. up to half the sampling frequency (f /2), excluding dc. The ratio S is dependent on the number of quantization levels in the digitiza- tion process; the more levels, the smaller the quantization noise. The theoretical signal to (noise + distortion) ratio for an ideal N-bit converter with a sine wave input is given by: Signal to (Noise + Distortion) = (6.02 N +1.76) dB Thus for a 12-bit converter, this is 74 dB. 1 AIN(+) refers to the positive input of the pseudo differential pair, and AIN(–) refers to the negative analog input of the pseudo differential pair or to AGND depending on the channel configuration. –8– REV. B AD7858/AD7858L ON-CHIP REGISTERS The AD7858/AD7858L powers up with a set of default conditions. The only writing required is to select the channel configuration. Without performing any other write operations the AD7858/AD7858L still retains the flexibility for performing a full power-down and a full self-calibration. Extra features and flexibility, such as performing different power-down options, different types of calibrations including system calibration, and software conversion start, can be selected by further writing to the part. The AD7858/AD7858L contains a Control Register, ADC Output Data Register, Status Register, Test Register, and 10 Calibration Registers. The control register is write-only, the ADC output data register and the status register are read-only, and the test and calibration registers are both read/write registers. The Test Register is used for testing the part and should not be written to. Addressing the On-Chip Registers Writing A write operation to the AD7858/AD7858L consists of 16 bits. The two MSBs, ADDR0 and ADDR1, are decoded to determine which register is addressed, and the subsequent 14 bits of data are written to the addressed register. It is not until all 16 bits are written that the data is latched into the addressed registers. Table I shows the decoding of the address bits while Figure 4 shows the overall write register hierarchy. Table I. Write Register Addressing ADDR1 ADDR0 Comment 0 0 This combination does not address any register so the subsequent 14 data bits are ignored. 0 1 This combination addresses the TEST REGISTER. The subsequent 14 data bits are written to the test register. 1 0 This combination addresses the CALIBRATION REGISTERS. The subsequent 14 data bits are written to the selected calibration register. 1 1 This combination addresses the CONTROL REGISTER. The subsequent 14 data bits are written to the control register. Reading To read from the various registers the user must first write to Bits 6 and 7 in the Control Register, RDSLT0 and RDSLT1. These bits are decoded to determine which register is addressed during a read operation. Table II shows the decoding of the read address bits while Figure 5 shows the overall read register hierarchy. The power-up status of these bits is 00 so that the default read will be from the ADC output data register. Once the read selection bits are set in the Control Register, all subsequent read operations that follow will be from the selected regis- ter until the read selection bits are changed in the Control Register. Table II. Read Register Addressing RDSLT1 RDSLT0 Comment 0 0 All successive read operations will be from ADC OUTPUT DATA REGISTER. This is the power-up default setting. There will always be 4 leading zeros when reading from the ADC Output Data Register. 0 1 All successive read operations will be from TEST REGISTER. 1 0 All successive read operations will be from CALIBRATION REGISTERS. 1 1 All successive read operations will be from STATUS REGISTER. RDSLT1, RDSLT0 ADDR1, ADDR0 DECODE DECODE 01 10 11 00 01 10 11 ADC OUTPUT TEST CALIBRATION STATUS TEST CALIBRATION CONTROL REGISTER REGISTERS REGISTER DATA REGISTER REGISTER REGISTERS REGISTER GAIN(1) GAIN(1) GAIN(1) GAIN(1) OFFSET(1) OFFSET(1) OFFSET(1) GAIN(1) OFFSET(1) GAIN(1) OFFSET(1) OFFSET(1) DAC(8) DAC(8) 00 01 10 11 00 01 10 11 CALSLT1, CALSLT0 CALSLT1, CALSLT0 DECODE DECODE Figure 4. Write Register Hierarchy/Address Decoding Figure 5. Read Register Hierarchy/Address Decoding REV. B –9– AD7858/AD7858L CONTROL REGISTER The arrangement of the Control Register is shown below. The control register is a write only register and contains 14 bits of data. The control register is selected by putting two 1s in ADDR1 and ADDR0. The function of the bits in the control register are de- scribed below. The power-up status of all bits is 0. MSB SGL/DIFF CH2 CH1 CH0 PMGT1 PMGT0 RDSLT1 RDSLT0 2/3 MODE CONVST CALMD CALSLT1 CALSLT0 STCAL LSB CONTROL REGISTER BIT FUNCTION DESCRIPTION Bit Mnemonic Comment 13 SGL/DIFF A 0 in this bit position configures the input channels in pseudo-differential mode. A 1 in this bit position configures the input channels in single-ended mode (see Table III). 12 CH2 These three bits are used to select the channel on which the conversion is performed. The channels can 11 CH1 be configured as eight single-ended channels or four pseudo-differential channels. The default selection 10 CH0 is AIN1 for the positive input and AIN2 for the negative input (see Table III for channel selection). 9 PMGT1 Power Management Bits. These two bits are used with the SLEEP pin for putting the part into various 8 PMGT0 Power-Down Modes (see Power-Down section for more details). 7 RDSLT1 Theses two bits determine which register is addressed for the read operations (see Table II). 6 RDSLT0 52/3 MODE Interface Mode Select Bit. With this bit set to 0, Interface Mode 2 is enabled. With this bit set to 1, Interface Mode 1 is enabled where DIN is used as an output as well as an input. This bit is set to 0 by default after every read cycle; thus when using the Two-Wire Interface Mode, this bit needs to be set to 1 in every write cycle. 4 CONVST Conversion Start Bit. A logic one in this bit position starts a single conversion, and this bit is automati- cally reset to 0 at the end of conversion. This bit may also be used in conjunction with system calibration (see Calibration section.) 3 CALMD Calibration Mode Bit. A 0 here selects self-calibration, and a 1 selects a system calibration (see Table IV). 2 CALSLT1 Calibration Selection Bits and Start Calibration Bit. These bits have two functions. 1 CALSLT0 With the STCAL bit set to 1 the CALSLT1 and CALSLT0 bits determine the type of calibration per 0 STCAL formed by the part (see Table IV). The STCAL bit is automatically reset to 0 at the end of calibration. With the STCAL bit set to 0 the CALSLT1 and CALSLT0 bits are decoded to address the calibration register for read/write of calibration coefficients (see section on the Calibration Registers for more details). –10– REV. B AD7858/AD7858L Table III. Channel Selection SGL/DIFF CH2 CH1 CH0 AIN(+)* AIN(–)* 0 0 0 0 AIN AIN 1 2 0 0 0 1 AIN AIN 3 4 0 0 1 0 AIN AIN 5 6 0 0 1 1 AIN AIN 7 8 0 1 0 0 AIN AIN 2 1 0 1 0 1 AIN AIN 4 3 0 1 1 0 AIN AIN 6 5 0 1 1 1 AIN AIN 8 7 1 0 0 0 AIN AGND 1 1 0 0 1 AIN AGND 3 1 0 1 0 AIN AGND 5 1 0 1 1 AIN AGND 7 1 1 0 0 AIN AGND 2 1 1 0 1 AIN AGND 4 1 1 1 0 AIN AGND 6 1 1 1 1 AIN AGND 8 *AIN(+) refers to the positive input seen by the AD7858/AD7858L sample and hold circuit, *AIN(–) refers to the negative input seen by the AD7858/AD7858L sample and hold circuit. Table IV. Calibration Selection CALMD CALSLT1 CALSLT0 Calibration Type 0 00A Full Internal Calibration is initiated where the Internal DAC is calibrated followed by the Internal Gain Error, and finally the Internal Offset Error is calibrated out. This is the default setting. 0 0 1 Here the Internal Gain Error is calibrated out followed by the Internal Offset Error calibrated out. 0 1 0 This calibrates out the Internal Offset Error only. 0 1 1 This calibrates out the Internal Gain Error only. 1 00A Full System Calibration is initiated here where first the Internal DAC is calibrated followed by the System Gain Error, and finally the System Offset Error is calibrated out. 1 0 1 Here the System Gain Error is calibrated out followed by the System Offset Error. 1 1 0 This calibrates out the System Offset Error only. 1 1 1 This calibrates out the System Gain Error only. REV. B –11– AD7858/AD7858L STATUS REGISTER The arrangement of the Status Register is shown below. The status register is a read-only register and contains 16 bits of data. The status register is selected by first writing to the control register and putting two 1s in RDSLT1 and RDSLT0. The function of the bits in the status register are described below. The power-up status of all bits is 0. START WRITE TO CONTROL REGISTER SETTING RDSLT0 = RDSLT1 = 1 READ STATUS REGISTER Figure 6. Flowchart for Reading the Status Register MSB ZERO BUSY SGL/DIFF CH2 CH1 CH0 PMGT1 PMGT0 RDSLT1 RDSLT0 2/3 MODE X CALMD CALSLT1 CALSLT0 STCAL LSB STATUS REGISTER BIT FUNCTION DESCRIPTION Bit Mnemonic Comment 15 ZERO This bit is always 0. 14 BUSY Conversion/Calibration Busy Bit. When this bit is 1, it indicates that there is a conversion or calibration in progress. When this bit is 0, there is no conversion or calibration in progress. 13 SGL/DIFF These four bits indicate the channel selected for conversion (see Table III). 12 CH2 11 CH1 10 CH0 9 PMGT1 Power management bits. These bits along with the SLEEP pin will indicate if the part is in a 8 PMGT0 power-down mode or not. See Table VI for description. 7 RDSLT1 Both of these bits are always 1, indicating it is the status register being read (see Table II). 6 RDSLT0 52/3 MODE Interface Mode Select Bit. With this bit at 0, the device is in Interface Mode 2. With this bit at 1, the device is in Interface Mode 1. This bit is reset to 0 after every read cycle. 4X Don’t care bit. 3 CALMD Calibration Mode Bit. A 0 in this bit indicates a self-calibration is selected, and a 1 in this bit indicates a system calibration is selected (see Table IV). 2 CALSLT1 Calibration Selection Bits and Start Calibration Bit. The STCAL bit is read as a 1 if a 1 CALSLT0 calibration is in progress and as a 0 if there is no calibration in progress. The CALSLT1 and 0 STCAL CALSLT0 bits indicate which of the calibration registers are addressed for reading and writing (see section on the Calibration Registers for more details). –12– REV. B AD7858/AD7858L CALIBRATION REGISTERS The AD7858/AD7858L has 10 calibration registers in all, eight for the DAC, one for the offset, and one for gain. Data can be written to or read from all 10 calibration registers. In self- and system calibration the part automatically modifies the calibration registers; only if the user needs to modify the calibration registers should an attempt be made to read from and write to the calibration registers. Addressing the Calibration Registers The calibration selection bits in the control register CALSLT1 and CALSLT0 determine which of the calibration registers are ad- dressed (see Table V). The addressing applies to both the read and write operations for the calibration registers. The user should not attempt to read from and write to the calibration registers at the same time. Table V. Calibration Register Addressing CALSLT1 CALSLT0 Comment 0 0 This combination addresses the Gain (1), Offset (1) and DAC Registers (8). Ten registers in total. 0 1 This combination addresses the Gain (1) and Offset (1) Registers. Two registers in total. 1 0 This combination addresses the Offset Register. One register in total. 1 1 This combination addresses the Gain Register. One register in total. Writing to/Reading from the Calibration Registers When reading from the calibration registers there will always be For writing to the calibration registers a write to the control two leading zeros for each of the registers. When operating in register is required to set the CALSLT0 and CALSLT1 bits. Serial Interface Mode 1 the read operations to the calibration For reading from the calibration registers a write to the control registers cannot be aborted. The full number of read operations register is required to set the CALSLT0 and CALSLT1 bits, must be completed (see section on Serial Interface Mode 1 but also to set the RDSLT1 and RDSLT0 bits to 10 (this ad- Timing for more detail). dresses the calibration registers for reading). The calibration register pointer is reset on writing to the control register setting START the CALSLT1 and CALSLT0 bits, or upon completion of all the calibration register write/read operations. When reset it WRITE TO CONTROL REGISTER SETTING STCAL = 0 points to the first calibration register in the selected write/read AND CALSLT1, CALSLT0 = 00, 01, 10, 11 sequence. The calibration register pointer will point to the gain calibration register upon reset in all but one case, this case being CAL REGISTER POINTER IS where the offset calibration register is selected on its own AUTOMATICALLY RESET (CALSLT1 = 1, CALSLT0 = 0). Where more than one calibra- tion register is being accessed the calibration register pointer will WRITE TO CAL REGISTER be automatically incremented after each calibration register (ADDR1 = 1, ADDR0 = 0) write/read operation. The order in which the 10 calibration registers are arranged is shown in Figure 7. The user may abort CAL REGISTER POINTER IS at any time before all the calibration register write/read opera- AUTOMATICALLY INCREMENTED tions are completed, and the next control register write opera- tion will reset the calibration register pointer. The flow chart in Figure 8 shows the sequence for writing to the calibration regis- LAST REGISTER ters and Figure 9 for reading. NO WRITE OPERATION OR ABORT CALIBRATION REGISTERS ? CAL REGISTER (1) GAIN REGISTER ADDRESS POINTER YES OFFSET REGISTER (2) FINISHED (3) DAC 1ST MSB REGISTER CALIBRATION REGISTER . . . ADDRESS POINTER . . . Figure 8. Flowchart for Writing to the Calibration Registers POSITION IS DETERMINED . . . BY THE NUMBER OF . . . CALIBRATION REGISTERS . . . ADDRESSED AND THE . . . NUMBER OF READ/WRITE . . . OPERATIONS DAC 8TH MSB REGISTER (10) Figure 7. Calibration Register Arrangements REV. B –13– AD7858/AD7858L Q. If a +20 mV offset is present in the analog input signal and the START reference voltage is 2.5 V what code needs to be written to the offset register to compensate for the offset? WRITE TO CONTROL REGISTER SETTING STCAL = 0, RDSLT1 = 1, A. 2.5 V reference implies that the resolution in the offset regis- RDSLT0 = 0, AND CALSLT1, CALSLT0 = 00, 01, 10, 11 13 ter is 5% × 2.5 V/2 = 0.015 mV. +20 mV/0.015 mV = 1310.72; rounding to the nearest number gives 1311. In CAL REGISTER POINTER IS AUTOMATICALLY RESET binary terms this is 0101 0001 1111. Therefore, decrease the offset register by 0101 0001 1111. This method of compensating for offset in the analog input READ CAL REGISTER signal allows for fine tuning the offset compensation. If the offset on the analog input signal is known, there will be no need CAL REGISTER POINTER IS to apply the offset voltage to the analog input pins and do a AUTOMATICALLY INCREMENTED system calibration. The offset compensation can take place in software. LAST Adjusting the Gain Calibration Register REGISTER NO READ The gain calibration register contains 16 bits, two leading 0s OPERATION and 14 data bits. The data bits are binary weighted as in the OR ABORT offset calibration register. The gain register value is effectively ? multiplied by the analog input to scale the conversion result YES over the full range. Increasing the gain register compensates for a smaller analog input range and decreasing the gain register FINISHED compensates for a larger input range. The maximum analog input range that the gain register can compensate for is 1.025 Figure 9. Flowchart for Reading from the Calibration times the reference voltage, and the minimum input range is Registers 0.975 times the reference voltage. Adjusting the Offset Calibration Register The offset calibration register contains 16 bits, two leading zeros, and 14 data bits. By changing the contents of the offset register different amounts of offset on the analog input signal can be compensated for. Increasing the number in the offset calibration register compensates for negative offset on the analog input signal, and decreasing the number in the offset calibration regis- ter compensates for positive offset on the analog input signal. The default value of the offset calibration register is 0010 0000 0000 0000 approximately. This is not an exact value, but the value in the offset register should be close to this value. Each of the 14 data bits in the offset register is binary weighted; the MSB has a weighting of 5% of the reference voltage, the MSB-1 has a weighting of 2.5%, the MSB-2 has a weighting of 1.25%, and so on down to the LSB which has a weighting of 0.0006%. This gives a resolution of ±0.0006% of V approximately. REF 13 More accurately the resolution is ±(0.05 × V )/2 volts = REF ±0.015 mV, with a 2.5 V reference. The maximum offset that can be compensated for is ±5% of the reference voltage, which equates to ±125 mV with a 2.5 V reference and ±250 mV with a 5 V reference. –14– REV. B AD7858/AD7858L CIRCUIT INFORMATION conversion will take 17.5 CLKIN periods. The maximum speci- The AD7858/AD7858L is a fast, 12-bit single supply A/D con- fied conversion time is 4.6 µs for the AD7858 (18t , CLKIN verter. The part requires an external 4 MHz/1.8 MHz master CLKIN = 4 MHz) and 10 µs for the AD7858L (18t , CLKIN clock (CLKIN), two C capacitors, a CONVST signal to start REF CLKIN = 1.8 MHz). When a conversion is completed, the conversion, and power supply decoupling capacitors. The part BUSY output goes low, and then the result of the conversion provides the user with track/hold, on-chip reference, calibration can be read by accessing the data through the serial interface. features, A/D converter, and serial interface logic functions on a To obtain optimum performance from the part, the read opera- single chip. The A/D converter section of the AD7858/AD7858L tion should not occur during the conversion or 400 ns prior to consists of a conventional successive-approximation converter the next CONVST rising edge. However, the maximum based around a capacitor DAC. The AD7858/AD7858L accepts throughput rates are achieved by reading/writing during conver- an analog input range of 0 to +V where the reference can be DD sion, and reading/writing during conversion is likely to degrade tied to V . The reference input to the part is buffered on-chip. DD the Signal to (Noise + Distortion) by only 0.5 dBs. The AD7858 can operate at throughput rates up to 200 kHz, 100 kHz for the A major advantage of the AD7858/AD7858L is that a conversion AD7858L. For the AD7858 a conversion takes 18 CLKIN can be initiated in software as well as applying a signal to the periods; 2 CLKIN periods are needed for the acquisition time CONVST pin. Another innovative feature of the AD7858/ giving a full cycle time of 5 µs (= 200 kHz, CLKIN = 4 MHz). AD7858L is self-calibration on power-up, which is initiated For the AD7858L 100 kHz throughput can be obtained as having a capacitor from the CAL pin to AGND, to give superior follows: the CLKIN and CONVST signals are arranged to give dc accuracy. See Automatic Calibration on Power-Up section. a conversion time of 16.5 CLKIN periods as described above, The part is available in a 24-pin SSOP package and this offers 1.5 CLKIN periods are allowed for the acquisition time. This the user considerable space-saving advantages over alternative gives a full cycle time of 10 µs (=100 kHz, CLKIN = 1.8 MHz). solutions. The AD7858L version typically consumes only When using the software conversion start for maximum through- 5.5 mW making it ideal for battery-powered applications. put the user must ensure the control register write operation extends beyond the falling edge of BUSY. The falling edge of CONVERTER DETAILS BUSY resets the CONVST bit to 0 and allows it to be repro- The master clock for the part must be applied to the CLKIN grammed to 1 to start the next conversion. pin. Conversion is initiated on the AD7858/AD7858L by pulsing the CONVST input or by writing to the control register and TYPICAL CONNECTION DIAGRAM setting the CONVST bit to 1. On the rising edge of CONVST Figure 10 shows a typical connection diagram for the AD7858/ (or at the end of the control register write operation), the on- AD7858L. The AGND and the DGND pins are connected chip track/hold goes from track to hold mode. The falling edge together at the device for good noise suppression. The CAL pin of the CLKIN signal that follows the rising edge of the CONVST has a 0.01 µF capacitor to enable an automatic self-calibration signal initiates the conversion, provided the rising edge of on power-up. The conversion result is output in a 16-bit word CONVST occurs at least 10 ns typically before this CLKIN with four leading zeros followed by the MSB of the 12-bit result. edge. The conversion cycle will take 16.5 CLKIN periods from Note that after the AV and DV power-up the part will DD DD this CLKIN falling edge. If the 10 ns setup time is not met, the 4MHz/1.8MHz OSCILLATOR 200kHz/100kHz PULSE GENERATOR MASTER CLOCK ANALOG SUPPLY INPUT +3V TO +5V 10�F 0.1�F 0.1�F CONVERSION START INPUT AV DV DD DD CLKIN OSCILLOSCOPE AIN(+) 0V TO 2.5V INPUT AIN(–) SCLK CH1 SERIAL CLOCK INPUT C REF1 CONVST 0.1�F CH2 AD7858/ C REF2 SYNC 0.01�F CH3 AD7858L FRAME SYNC INPUT DV SLEEP DIN CH4 DD SERIAL DATA INPUT CAL 0.01�F CH5 DOUT AGND SERIAL DATA OUTPUT AUTO CAL ON DGND POWER-UP 4 LEADING INTERNAL/ DATA GENERATOR ZEROS FOR 0.1�F EXTERNAL ADC DATA REFERENCE OPTIONAL AD780/ EXTERNAL PULSE GENERATOR REF-192 REFERENCE Figure 10. Typical Circuit REV. B –15– AD7858/AD7858L require approximately 150 ms for the internal reference to settle For ac applications, removing high frequency components from and for the automatic calibration on power-up to be completed. the analog input signal is recommended by use of an RC low- pass filter on the AIN(+) pin as shown in Figure 13. In applica- For applications where power consumption is a major concern tions where harmonic distortion and signal to noise ratio are then the SLEEP pin can be connected to DGND. See Power- critical the analog input should be driven from a low impedance Down section for more detail on low power applications. source. Large source impedances will significantly affect the ac performance of the ADC. This may necessitate the use of an ANALOG INPUT input buffer amplifier. The choice of the op amp will be a func- The equivalent circuit of the analog input section is shown in tion of the particular application. Figure 11. During the acquisition interval the switches are both in the track position and the AIN(+) charges the 20 pF capacitor When no amplifier is used to drive the analog input the source through the 125 Ω resistance. On the rising edge of CONVST impedance should be limited to low values. The maximum switches SW1 and SW2 go into the hold position retaining source impedance will depend on the amount of total harmonic charge on the 20 pF capacitor as a sample of the signal on distortion (THD) that can be tolerated. The THD will increase AIN(+). The AIN(–) is connected to the 20 pF capacitor, and as the source impedance increases and performance will de- this unbalances the voltage at node A at the input of the com- grade. Figure 12 shows a graph of the total harmonic distortion parator. The capacitor DAC adjusts during the remainder of the versus analog input signal frequency for different source imped- conversion cycle to restore the voltage at node A to the correct ances. With the setup as in Figure 13, the THD is at the –90 dB value. This action transfers a charge, representing the analog level. With a source impedance of 1 kΩ and no capacitor on the input signal, to the capacitor DAC which in turn forms a digital AIN(+) pin, the THD increases with frequency. representation of the analog input signal. The voltage on the –72 AIN(–) pin directly influences the charge transferred to the THD vs. FREQUENCY FOR DIFFERENT capacitor DAC at the hold instant. If this voltage changes dur- SOURCE IMPEDANCES ing the conversion period, the DAC representation of the analog –76 input voltage will be altered. Therefore it is most important that the voltage on the AIN(–) pin remains constant during the conver- R = 1k� IN sion period. Furthermore it is recommended that the AIN(–) –80 pin is always connected to AGND or to a fixed dc voltage. Acquisition Time –84 The track and hold amplifier enters its tracking mode on the R = 50�, 10nF IN AS IN FIGURE 13 falling edge of the BUSY signal. The time required for the track and hold amplifier to acquire an input signal will depend on –88 how quickly the 20 pF input capacitance is charged. The acqui- sition time is calculated using the formula: –92 0 20 40 60 80 100 t = 9 × (R + 125 Ω)× 20 pF ACQ IN INPUT FREQUENCY – kHz where R is the source impedance of the input signal, and IN Figure 12. THD vs. Analog Input Frequency 125 Ω, 20 pF is the input R, C. In a single supply application (both 3 V and 5 V), the V+ and V– of the op amp can be taken directly from the supplies to the TRACK 125� AIN(+) AD7858/AD7858L which eliminates the need for extra external AIN(–) SW1 power supplies. When operating with rail-to-rail inputs and 125� HOLD CAPACITOR outputs, at frequencies greater than 10 kHz care must be taken DAC 20pF in selecting the particular op amp for the application. In particu- lar for single supply applications the input amplifiers should be NODE A connected in a gain of –1 arrangement to get the optimum per- SW2 formance. Figure 13 shows the arrangement for a single supply COMPARATOR HOLD TRACK application with a 50 Ω and 10 nF low-pass filter (cutoff fre- C quency 320 kHz) on the AIN(+) pin. Note that the 10 nF is a REF2 capacitor with good linearity to ensure good ac performance. Figure 11. Analog Input Equivalent Circuit Recommended single supply op amps are the AD820 and the DC/AC Applications AD820-3 V. For dc applications high source impedances are acceptable +3V TO +5V provided there is enough acquisition time between conversions 10�F 0.1�F 10k� to charge the 20 pF capacitor. The acquisition time can be calculated from the above formula for different source imped- V 10k� IN V+ 50� ances. For example with R = 5 kΩ, the required acquisition (0 TO V ) IN TO AIN(+) OF REF 10k� AD7858/AD7858L time will be 922 ns. V 10nF REF AD820 V+ (NPO) AD820-3V 10k� Figure 13. Analog Input Buffering –16– REV. B THD – dB AD7858/AD7858L REFERENCE SECTION Input Range For specified performance, it is recommended that when using The analog input range for the AD7858/AD7858L is 0 V to an external reference this reference should be between 2.3 V V . The AIN(–) pin on the AD7858/AD7858L can be biased REF and the analog supply AV . The connections for the relevant up above AGND, if required. The advantage of biasing the DD reference pins are shown in the typical connection diagrams. If lower end of the analog input range away from AGND is that the internal reference is being used, the REF /REF pin the user does not need to have the analog input swing all the IN OUT should have a 100 nF capacitor connected to AGND very close way down to AGND. This has the advantage in true single- to the REF /REF pin. These connections are shown in supply applications that the input amplifier does not need to IN OUT Figure 16. swing all the way down to AGND. The upper end of the analog input range is shifted up by the same amount. Care must be If the internal reference is required for use external to the ADC, taken so that the bias applied does not shift the upper end of the it should be buffered at the REF /REF pin and a 100 nF IN OUT analog input above the AV supply. In the case where the DD connected from this pin to AGND. The typical noise performance reference is the supply, AV , the AIN(–) must be tied to DD for the internal reference, with 5 V supplies, is 150 nV/√Hz @ AGND. 1 kHz and dc noise is 100 µV p-p. ANALOG SUPPLY TRACK AND HOLD +3V TO +5V AIN(+) AMPLIFIER 10�F 0.1�F 0.1�F V = 0 TO V STRAIGHT IN REF DOUT BINARY AIN(–) FORMAT AV DV DD DD C REF1 AD7858/ 0.1�F AD7858L AD7858/ AD7858L C REF2 Figure 14. 0 to V Input Configuration REF 0.01�F Transfer Function For the AD7858/AD7858L input range the designed code tran- REF /REF IN OUT 0.1�F sitions occur midway between successive integer LSB values (i.e., 1/2 LSB, 3/2 LSBs, 5/2 LSBs . . . FS – 3/2 LSBs). The output coding is straight binary with 1 LSB = FS/4096 = 3.3 V/ Figure 16. Relevant Connections When Using Internal 4096 = 0.8 mV when V = 3.3 V. The ideal input/output REF Reference transfer characteristic is shown in Figure 15. The other option is that the REF /REF pin be overdriven IN OUT OUTPUT by connecting it to an external reference. This is possible due to CODE the series resistance from the REF /REF pin to the internal IN OUT 111...111 reference. This external reference can have a range that includes 111...110 AV . When using AV as the reference source, the 100 nF DD DD 111...101 capacitor from the REF /REF pin to AGND should be as IN OUT 111...100 close as possible to the REF /REF pin, and also the C IN OUT REF1 pin should be connected to AV to keep this pin at the same DD level as the reference. The connections for this arrangement are shown in Figure 17. When using AV it may be necessary to DD add a resistor in series with the AV supply. This will have the DD 000...011 FS 1LSB = effect of filtering the noise associated with the AV supply. DD 4096 000...010 000...001 ANALOG SUPPLY +3V TO +5V 000...000 10�F 0.1�F 0.1�F 0V 1LSB +FS –1LSB V = (AIN(+) – AIN(–)), INPUT VOLTAGE IN AV DV DD DD Figure 15. AD7858/AD7858L Transfer Characteristic C REF1 0.1�F AD7858/ AD7858L C REF2 0.01�F REF /REF IN OUT 0.1�F Figure 17. Relevant Connections When Using AV as the DD Reference REV. B –17– AD7858/AD7858L PERFORMANCE CURVES –78 AV = DV = 3.3V/5.0V, DD DD Figure 18 shows a typical FFT plot for the AD7858 at 200 kHz 100mVp-p SINE WAVE ON AV DD sample rate and 10 kHz input frequency. –80 0 –82 AV = DV = 3.3V DD DD f = 200kHz SAMPLE 3.3V –20 f = 10kHz IN –84 SNR = 72.04dB THD = –88.43dB –40 –86 5.0V –60 –88 –80 –90 0 20 40 60 80 100 INPUT FREQUENCY – kHz –100 Figure 20. PSRR vs. Frequency –120 0 20 40 60 80 100 POWER-DOWN OPTIONS FREQUENCY – kHz The AD7858 provides flexible power management to allow the Figure 18. FFT Plot user to achieve the best power performance for a given through- put rate. The power management options are selected by Figure 19 shows the SNR vs. Frequency for different supplies programming the power management bits, PMGT1 and PMGT0, and different external references. in the control register and by use of the SLEEP pin. Table VI summarizes the power-down options that are available and how 74 AV = DV WITH 2.5V REFERENCE DD DD they can be selected by using either software, hardware, or a UNLESS STATED OTHERWISE combination of both. The AD7858 can be fully or partially 73 powered down. When fully powered down, all the on-chip cir- cuitry is powered down and I is 1 µA typ. If a partial power- 5.0V SUPPLIES, WITH 5V REFERENCE DD down is selected, then all the on-chip circuitry except the reference 72 5.0V SUPPLIES is powered down and I is 400 µA typ. The choice of full or par- DD tial power-down does not give any significant improvement in 5.0V SUPPLIES, L VERSION 71 throughput with a power-down between conversions. This is discussed in the next section–Power-Up Times. However, a 3.3V SUPPLIES partial power-down does allow the on-chip reference to be used 70 externally even though the rest of the AD7858 circuitry is pow- ered down. It also allows the AD7858 to be powered up faster after a long power-down period when using the on-chip refer- 69 0 20 40 60 80 100 ence (See Power-Up Times–Using On-Chip Reference). INPUT FREQUENCY – kHz When using the SLEEP pin, the power management bits PMGT1 Figure 19. SNR vs. Frequency and PMGT0 should be set to zero (default status on power-up). Figure 20 shows the Power Supply Rejection Ratio vs. Fre- Bringing the SLEEP pin logic high ensures normal operation, quency for the part. The Power Supply Rejection Ratio is de- and the part does not power down at any stage. This may be fined as the ratio of the power in adc output at frequency f to necessary if the part is being used at high throughput rates when the power of a full-scale sine wave. it is not possible to power down between conversions. If the user wishes to power down between conversions at lower throughput PSRR (dB) = 10 log (Pf/Pfs) rates (i.e. <100 kSPS for the AD7858) to achieve better power Pf = Power at frequency f in adc output, Pfs = power of a performances, then the SLEEP pin should be tied logic low. full-scale sine wave. Here a 100 mV peak-to-peak sine wave is If the power-down options are to be selected in software only, coupled onto the AV supply while the digital supply is left DD then the SLEEP pin should be tied logic high. By setting the unaltered. Both the 3.3 V and 5.0 V supply performances are power management bits PMGT1 and PMGT0 as shown in shown. Table VI, a Full Power-Down, Full Power-Up, Full Power- Down Between Conversions, and a Partial Power-Down Be- tween Conversions can be selected. –18– REV. B S(N+D) RATIO – dB SNR – dB PSRR – dB AD7858/AD7858L Table VI. Power Management Options a logic high. If the autocalibration is disabled, then the user must take into account the time required by the AD7858 to power-up PMGT1 PMGT0 SLEEP before a self-calibration is carried out. This power-up time is the Bit Bit Pin Comment time taken for the AD7858 to power up when power is first applied (300 µs) typ) or the time it takes the external reference 00 0 Full Power-Down if Not to settle to the 12-bit level–whichever is the longer. Calibrating or Converting (Default Condition The AD7858 powers up from a full hardware or software After Power-On) power-down in 5 µs typ. This limits the throughput which the 00 1 Normal Operation part is capable of to 104 kSPS for the AD7858 operating with a 01 X Normal Operation 4 MHz CLK and 66 kSPS for the AD7858L with a 1.8 MHz (Independent of the SLEEP Pin) CLK when powering down between conversions. Figure 22 10 X Full Power-Down shows how power-down between conversions is implemented 11 X Partial Power-Down if Not using the CONVST pin. The user first selects the power-down Converting between conversions option by using the SLEEP pin and the power management bits, PMGT1 and PMGT0, in the control A typical connection diagram for a low power application is register, (see last section). In this mode the AD7858 automati- shown in Figure 21 (AD7858L is the low power version of the cally enters a full power-down at the end of a conversion, i.e., AD7858). when BUSY goes low. The falling edge of the next CONVST pulse causes the part to power up. Assuming the external refer- CURRENT, ence is left powered up, the AD7858 should be ready for normal I = 1.5mA 1.8MHz TYP 0.1�F operation 5 µs after this falling edge. The rising edge of CONVST ANALOG OSCILLATOR SUPPLY initiates a conversion so the CONVST pulse should be at least 10�F 0.1�F +3V 5 µs wide. The part automatically powers down on completion of the conversion. MASTER AV DV CLOCK 100kHz DD DD INPUT PULSE START CONVERSION ON RISING EDGE 0V TO 2.5V AIN(+) CLKIN GENERATOR INPUT POWER-UP ON FALLING EDGE AIN(–) AD7858/ 5�s AD7858L C REF1 CONVERSION 0.1�F CONVST START INPUT CONVST t CONVERT C REF2 SERIAL CLOCK 0.01�F INPUT BUSY SCLK AUTO POWER DOWN AFTER SLEEP POWER-UP NORMAL FULL POWER-UP SYNC CONVERSION TIME OPERATION POWER-DOWN TIME LOW CAL POWER SERIAL DATA 0.01�F �C/�P Figure 22. Power-Up Timing When Using CONVST Pin OUTPUT DOUT AUTO CAL ON NOTE: Where the software CONVST is used or automatic full AGND SERIAL DATA POWER-UP INPUT power-down, the part must be powered up in software with an DGND DIN extra write setting PMGT1 = 0 and PMGT0 = 1 before a con- REF /REF IN OUT version is initiated in the next write. Automatic partial power- INTERNAL down after a calibration is not possible; the part must be REFERENCE 0.1�F powered down manually. If software calibrations are to be used when operating in the partial power-down mode, then three OPTIONAL separate writes are required. The first initiates the type of cali- REF192 EXTERNAL REFERENCE bration required, the second write powers the part down into partial power-down mode, while the third write powers the part Figure 21. Typical Low Power Circuit up again before the next calibration command is issued. Using the Internal (On-Chip) Reference POWER-UP TIMES As in the case of an external reference, the AD7858 can power- Using an External Reference up from one of two conditions, power-up after the supplies are When the AD7858 is powered up, the part is powered up from connected or power-up from hardware/software power-down. one of two conditions. First, when the power supplies are ini- When using the on-chip reference and powering up when AV DD tially powered up and, secondly, when the part is powered up and DV are first connected, it is recommended that the power- DD from either a hardware or software power-down (see last section). up calibration mode be disabled as explained above. When using When AV and DV are powered up, the AD7858 should be DD DD the on-chip reference, the power-up time is effectively the time left idle for approximately 32 ms (4 MHz CLK) to allow for the it takes to charge up the external capacitor on the REF /REF IN OUT autocalibration if a 10 nF cap is placed on the CAL pin, (see pin. This time is given by the equation: Calibration section). During power-up the functionality of the t = 9 × R × C UP SLEEP pin is disabled, i.e., the part will not power down until the end of the calibration if SLEEP is tied logic low. The auto- where R ≅ 150 kΩ and C = external capacitor. calibration on power-up can be disabled if the CAL pin is tied to REV. B –19– AD7858/AD7858L The recommended value of the external capacitor is 100 nF; 10 this gives a power-up time of approximately 135 ms before a calibration is initiated and normal operation should commence. AD7858 (4MHz CLK) When C is fully charged, the power-up time from a hardware REF or software power-down reduces to 5 µs. This is because an 1 internal switch opens to provide a high impedance discharge path for the reference capacitor during power-down—see Figure 23. An added advantage of the low charge leakage from the AD7858L (1.8MHz CLK) reference capacitor during power-down is that even though the 0.1 reference is being powered down between conversions, the reference capacitor holds the reference voltage to within 0.5 LSBs with throughput rates of 100 samples/second and over with a full power-down between conversions. A high input 0.01 impedance op amp like the AD707 should be used to buffer this 0515 25 35 45 10 20 30 40 50 reference capacitor if it is being used externally. Note, if the THROUGHPUT – kSPS AD7858 is left in its power-down state for more than 100 ms, Figure 24. Power vs. Throughput Rate the charge on C will start to leak away and the power-up REF time will increase. If this long power-up time is a problem, the CALIBRATION SECTION user can use a partial power-down for the last conversion so the Calibration Overview reference remains powered up. The automatic calibration that is performed on power-up en- sures that the calibration options covered in this section will not be required in a significant amount of applications. The user SWITCH OPENS will not have to initiate a calibration unless the operating condi- AD7858 DURING POWER-DOWN tions change (CLKIN frequency, analog input mode, reference REF /REF IN OUT ON-CHIP voltage, temperature, and supply voltages). The AD7858/ REFERENCE EXTERNAL AD7858L have a number of calibration features that may be CAPACITOR required in some applications and there are a number of advan- TO OTHER BUF CIRCUITRY tages in performing these different types of calibration. First, the internal errors in the ADC can be reduced significantly to give superior dc performance, and secondly, system offset and Figure 23. On-Chip Reference During Power-Down gain errors can be removed. This allows the user to remove reference errors (whether it be internal or external reference) POWER VS. THROUGHPUT RATE and to make use of the full dynamic range of the AD7858/ The main advantage of a full power-down after a conversion is AD7858L by adjusting the analog input range of the part for a that it significantly reduces the power consumption of the part specific system. at lower throughput rates. When using this mode of operation, There are two main calibration modes on the AD7858/AD7858L, the AD7858 is only powered up for the duration of the conver- self-calibration and system calibration. There are various op- sion. If the power-up time of the AD7858 is taken to be 5 µs tions in both self-calibration and system calibration as outlined and it is assumed that the current during power-up is 4 mA typ, previously in Table IV. All the calibration functions can be then power consumption as a function of throughput can easily initiated by pulsing the CAL pin or by writing to the control be calculated. The AD7858 has a conversion time of 4.6 µs register and setting the STCAL bit to one. The timing diagrams with a 4 MHz external clock. This means the AD7858 con- that follow involve using the CAL pin. sumes 4 mA typ, (or 12 mW typ V = 3 V) for 9.6 µs in every DD The duration of each of the different types of calibrations is conversion cycle if the device is powered down at the end of a given in Table VIII for the AD7858 with a 4 MHz master clock. conversion. If the throughput rate is 1 kSPS, the cycle time is These calibration times are master clock dependent. Therefore, 1000 µs and the average power dissipated during each cycle is the calibrating times for the AD7858L (CLKIN = 1.8 MHz) (9.6/1000) × (12 mW) = 115 µW. The graph, Figure 24, shows will be longer than those quoted in Table VIII. the power consumption of the AD7858 as a function of through- put. Table VII lists the power consumption for various through- Table VIII. Calibration Times (AD7858 with 4 MHz CLKIN) put rates. Type of Self- or Table VII. Power Consumption vs. Throughput System Calibration Time Throughput Rate Power Full 31.25 ms Offset + Gain 6.94 ms 1 kSPS 115 µW Offset 3.47 ms 10 kSPS 1.15 mW Gain 3.47 ms –20– REV. B POWER – mW AD7858/AD7858L Automatic Calibration on Power-On For the self- (gain + offset), self-offset, and self-gain calibrations The CAL pin has a 0.15 µA pull-up current source connected the BUSY line will be triggered high by the rising edge of the to it internally to allow for an automatic full self-calibration on CAL signal (or the end of the write to the control register if power-on. A full self-calibration will be initiated on power-on if calibration is initiated in software) and will stay high for the a capacitor is connected from the CAL pin to DGND. The full duration of the self-calibration. The length of time that internal current source connected to the CAL pin charges up the BUSY is high will depend on the type of self-calibration the external capacitor and the time required to charge the exter- that is initiated. Typical figures are given in Table VIII. The nal capacitor will depend on the size of the capacitor itself. This timing diagrams for the other self-calibration options will be time should be large enough to ensure that the internal refer- similar to that outlined in Figure 25. ence is settled before the calibration is performed. A 33 nF capacitor is sufficient to ensure that the internal reference has t = 100ns MIN, 1 settled (see Power-Up Times) before a calibration is initiated t = 2.5 t MAX, 15 CLKIN t = 125013 t CAL CLKIN taking into account trigger level and current source variations t 1 on the CAL pin. However, if an external reference is being used, this reference must have stabilized before the automatic CAL (I/P) calibration is initiated (a larger capacitor on the CAL pin t 15 should be used if the external reference has not settled when the autocalibration is initiated). Once the capacitor on the CAL pin BUSY (O/P) has charged, the calibration will be performed which will take t CAL 32 ms (4 MHz CLKIN). Therefore the autocalibration should be complete before operating the part. After calibration, the Figure 25. Timing Diagram for Full Self-Calibration part is accurate to the 12-bit level and the specifications quoted System Calibration Description on the data sheet apply. There will be no need to perform System calibration allows the user to take out system errors another calibration unless the operating conditions change or external to the AD7858/AD7858L as well as calibrate the errors unless a system calibration is required. of the AD7858/AD7858L itself. The maximum calibration Self-Calibration Description range for the system offset errors is ±5% of V and for the REF There are four different calibration options within the self- system gain errors is ±2.5% of V . This means that the maxi- REF calibration mode. First, there is a full self-calibration where the mum allowable system offset voltage applied between the DAC, internal gain, and internal offset errors are calibrated out. AIN(+) and AIN(–) pins for the calibration to adjust out this Then, there is the (Gain + Offset) self-calibration which cali- error is ±0.05 × V (i.e., the AIN(+) can be 0.05 × V above REF REF brates out the internal gain error and then the internal offset AIN(–) or 0.05 × V below AIN(–)). For the System gain error REF errors. The internal DAC is not calibrated here. Finally, there the maximum allowable system full-scale voltage that can be are the self-offset and self-gain calibrations which calibrate out applied between AIN(+) and AIN(–) for the calibration to the internal offset errors and the internal gain errors respectively. adjust out this error is V ± 0.025 × V ( i.e., the AIN(+) REF REF above AIN(–)). If the system offset or system gain errors are The internal capacitor DAC is calibrated by trimming each of outside the ranges mentioned the system calibration algorithm the capacitors in the DAC. It is the ratio of these capacitors to will reduce the errors as much as the trim range allows. each other that is critical, and so the calibration algorithm en- sures that this ratio is at a specific value by the end of the cali- Figures 26 through 28 illustrate why a specific type of system bration routine. For the offset and gain there are two separate calibration might be used. Figure 26 shows a system offset capacitors, one of which is trimmed when an offset or gain calibration (assuming a positive offset) where the analog input calibration is performed. Again, it is the ratio of these capacitors range has been shifted upwards by the system offset after the to the capacitors in the DAC that is critical and the calibration system offset calibration is completed. A negative offset may algorithm ensures that this ratio is at a specified value for both also be accounted for by a system offset calibration. the offset and gain calibrations. MAX SYSTEM FULL SCALE The zero-scale error is adjusted for an offset calibration, and IS �2.5% FROM V REF the positive full-scale error is adjusted for a gain calibration. V + SYS OFFSET REF V –1LSB V – 1LSB REF Self-Calibration Timing REF SYSTEM OFFSET The diagram of Figure 25 shows the timing for a full self- ANALOG ANALOG INPUT INPUT calibration. Here the BUSY line stays high for the full length of RANGE RANGE CALIBRATION the self-calibration. A self-calibration is initiated by bringing the SYS OFFSET SYS OFFSET CAL pin low (which initiates an internal reset) and then high AGND AGND again or by writing to the control register and setting the STCAL MAX SYSTEM OFFSET MAX SYSTEM OFFSET bit to 1 (note that if the part is in a power-down mode the CAL pulse- IS �5% OF V IS �5% OF V REF REF width must take account of the power-up time ). The BUSY line is Figure 26. System Offset Calibration triggered high from the rising edge of CAL (or the end of the write to the control register if calibration is initiated in soft- ware), and BUSY will go low when the full self-calibration is complete after a time t as shown in Figure 25. CAL REV. B –21– AD7858/AD7858L Figure 27 shows a system gain calibration (assuming a system system (gain + offset) calibrations will be sufficient. If the sys- full scale greater than the reference voltage) where the analog tem errors are large (close to the specified limits of the calibra- input range has been increased after the system gain calibration tion range) three system (gain + offset) calibrations may be is completed. A system full-scale voltage less than the reference required to reduced the offset and gain errors to at least the 12- voltage may also be accounted for by a system gain calibration. bit level. There will never be any need to perform more than three system (offset + gain) calibrations. MAX SYSTEM FULL SCALE MAX SYSTEM FULL SCALE The zero scale error is adjusted for an offset calibration and the IS �2.5% FROM V IS �2.5% FROM V REF REF positive full-scale error is adjusted for a gain calibration. SYS F.S. SYS F.S. V – 1LSB V – 1LSB REF REF System Calibration Timing SYSTEM GAIN ANALOG ANALOG The calibration timing diagram in Figure 29 is for a full system INPUT INPUT calibration where the falling edge of CAL initiates an internal RANGE RANGE CALIBRATION reset before starting a calibration (note that if the part is in power- AGND AGND down mode the CAL pulsewidth must take account of the power-up Figure 27. System Gain Calibration time). If a full system calibration is to be performed in software it is easier to perform separate gain and offset calibrations so Finally in Figure 28 both the system offset and gain are ac- that the CONVST bit in the control register does not have to be counted for by the a system offset followed by a system gain programmed in the middle of the system calibration sequence. calibration. First the analog input range is shifted upwards by The rising edge of CAL starts calibration of the internal DAC the positive system offset and then the analog input range is and causes the BUSY line to go high. If the control register is adjusted at the top end to account for the system full scale. set for a full system calibration, the CONVST must be used also. The full-scale system voltage should be applied to the MAX SYSTEM FULL SCALE MAX SYSTEM FULL SCALE IS �2.5% FROM V IS �2.5% FROM V REF REF analog input pins from the start of calibration. The BUSY line V + SYS OFFSET SYS F.S. REF will go low once the DAC and System Gain Calibration are V –1LSB SYS F.S. REF complete. Next the system offset voltage is applied to the AIN V – 1LSB REF SYSTEM OFFSET pin for a minimum setup time (t ) of 100 ns before the SETUP CALIBRATION ANALOG ANALOG FOLLOWED BY rising edge of the CONVST and remain until the BUSY signal INPUT INPUT RANGE RANGE goes low. The rising edge of the CONVST starts the system SYSTEM GAIN offset calibration section of the full system calibration and also CALIBRATION SYS OFFSET SYS OFFSET causes the BUSY signal to go high. The BUSY signal will go AGND AGND low after a time t when the calibration sequence is com- CAL2 MAX SYSTEM OFFSET MAX SYSTEM OFFSET plete. In some applications not all the input channels may be IS �5% OF V IS �5% OF V REF REF used. In this case it may be useful to dedicate two input chan- Figure 28. System (Gain + Offset) Calibration nels for the system calibration, one which has the system offset voltage applied to it, and one which has the system full scale System Gain and Offset Interaction voltage applied to it. When a system offset or gain calibration is The inherent architecture of the AD7858/AD7858L leads to an performed, the channel selected should correspond to the sys- interaction between the system offset and gain errors when a tem offset or system full-scale voltage channel. system calibration is performed. Therefore, it is recommended to perform the cycle of a system offset calibration followed by a The timing for a system (gain + offset) calibration is very similar system gain calibration twice. Separate system offset and system to that of Figure 29 the only difference being that the time t CAL1 gain calibrations reduce the offset and gain errors to at least the will be replaced by a shorter time of the order of t as the CAL2 12-bit level. By performing a system offset CAL first and a internal DAC will not be calibrated. The BUSY signal will system gain calibration second, priority is given to reducing the signify when the gain calibration is finished and when the part is gain error to zero before reducing the offset error to zero. If the ready for the offset calibration. system errors are small, a system offset calibration would be performed, followed by a system gain calibration. If the system t = 100ns MIN, t = 50/90ns MIN 5V/3V, 1 14 t = 2.5 t MAX, t = 111114 t , errors are large (close to the specified limits of the calibration 15 CLKIN CAL1 CLKIN t = 13899 t CAL2 CLKIN range), this cycle would be repeated twice to ensure that the offset and gain errors were reduced to at least the 12-bit level. t 1 The advantage of doing separate system offset and system gain CAL (I/P) calibrations is that the user has more control over when the t 15 analog inputs need to be at the required levels, and the BUSY (O/P) CONVST signal does not have to be used. t CAL2 t CAL1 t 16 Alternatively, a system (gain + offset) calibration can be CONVST (I/P) performed. It is recommended to perform three system (gain + t offset) calibrations to reduce the offset and gain errors to the SETUP 12-bit level. For the system (gain + offset) calibration priority is AIN (I/P) V V SYSTEM FULL SCALE OFFSET given to reducing the offset error to zero before reducing the Figure 29. Timing Diagram for Full System Calibration gain error to zero. Thus if the system errors are small then two –22– REV. B AD7858/AD7858L The timing diagram for a system offset or system gain calibra- Resetting the Serial Interface tion is shown in Figure 30. Here again the CAL is pulsed and When writing to the part via the DIN line there is the possibility the rising edge of the CAL initiates the calibration sequence (or of writing data into the incorrect registers, such as the test regis- the calibration can be initiated in software by writing to the ter for instance, or writing the incorrect data and corrupting the control register). The rising edge of the CAL causes the BUSY serial interface. The SYNC pin acts as a reset. Bringing the line to go high and it will stay high until the calibration se- SYNC pin high resets the internal shift register. The first data quence is finished. The analog input should be set at the correct bit after the next SYNC falling edge will now be the first bit of a level for a minimum setup time (t ) of 100 ns before the rising SETUP new 16-bit transfer. It is also possible that the test register con- edge of CAL and stay at the correct level until the BUSY signal tents were altered when the interface was lost. Therefore, once goes low. the serial interface is reset it may be necessary to write the 16-bit word 0100 0000 0000 0010 to restore the test register to its t default value. Now the part and serial interface are completely 1 reset. It is always useful to retain the ability to program the CAL (I/P) SYNC line from a port of the µController/DSP to have the t 15 ability to reset the serial interface. BUSY (O/P) Table X summarizes the interface modes provided by the t AD7858/AD7858L. It also outlines the various µP/µC to which CAL2 t SETUP the particular interface is suited. V OR V AIN (I/P) SYSTEM FULL SCALE SYSTEM OFFSET Interface Mode 1 may only be set by programming the control register (see section on Control Register). Figure 30. Timing Diagram for System Gain or System Some of the more popular µProcessors, µControllers, and the Offset Calibration DSP machines that the AD7858/AD7858L will interface to directly are mentioned here. This does not cover all µCs, µPs, SERIAL INTERFACE SUMMARY and DSPs. A more detailed timing description on each of the Table IX details the two interface modes and the serial clock interface modes follows. edges from which the data is clocked out by the AD7858/ AD7858L (DOUT Edge) and that the data is latched in on Table X. Interface Mode Description (DIN Edge). In both interface Modes 1 and 2 the SYNC is gated with the Interface �Processor/ SCLK. Thus the SYNC↓ may clock out the MSB of data. Sub- Mode �Controller Comment sequent bits will be clocked out by the Serial Clock, SCLK. The 1 8XC51 (2-Wire) condition for the SYNC↓ clocking out the MSB of data is as 8XL51 (DIN Is an Input/ follows: PIC17C42 Output Pin) The falling edge of SYNC will clock out the MSB if the serial clock 2 68HC11 (3-Wire, SPI) is low when the SYNC goes low. 68L11 (Default Mode) If this condition is not the case, the SCLK will clock out the 68HC16 MSB. If a noncontinuous SCLK is used, it should idle high. PIC16C64 ADSP21xx Table IX. SCLK Active Edges DSP56000 DSP56001 Interface Mode DSP56002 Edge DOUT Edge DIN DSP56L002 1, 2 SCLK↓ SCLK↑ REV. B –23– AD7858/AD7858L DETAILED TIMING SECTION automatically revert back to an input after a time, t . Note that 14 Mode 1 (2-Wire 8051 Interface) a continuous SCLK shown by the dotted waveform in Figure 35 The read and writing takes place on the DIN line and the con- can be used provided that the SYNC is low for only 16 clock version is initiated by pulsing the CONVST pin (note that in pulses in each of the read and write cycles. every write cycle the 2/3 MODE bit must be set to 1). The In Figure 32 the SYNC line is tied low permanently and this conversion may be started by setting the CONVST bit in the results in a different timing arrangement. With SYNC tied low control register to 1 instead of using the CONVST pin. permanently the DIN pin will never be three-stated. The 16th Below in Figure 31 and in Figure 32 are the timing diagrams for rising edge of SCLK configures the DIN pin as an input or an Operating Mode 1 in Table X where we are in the 2-wire inter- output as shown in the diagram. Here no more than 16 SCLK face mode. Here the DIN pin is used for both input and output pulses must occur for each of the read and write operations. as shown. The SYNC input is level triggered active low and can If reading from and writing to the calibration registers in this be pulsed (Figure 31) or can be constantly low (Figure 32). interface mode, all the selected calibration registers must be In Figure 31 the part samples the input data on the rising edge read from or written to. The read and write operations cannot of SCLK. After the 16th rising edge of SCLK the DIN is con- be aborted. When reading from the calibration registers, the figured as an output. When the SYNC is taken high the DIN is DIN pin will remain as an output for the full duration of all the three-stated. Taking SYNC low disables the three-state on the calibration register read operations. When writing to the calibra- DIN pin and the first SCLK falling edge clocks out the first data tion registers, the DIN pin will remain as an input for the full bit. Once the 16 clocks have been provided the DIN pin will duration of all the calibration register write operations. t = –0.4t MIN (NONCONTINUOUS SCLK) �0.4t ns MIN/MAX (CONTINUOUS SCLK), 3 SCLK SCLK t = 75/115ns MAX (5V/3V), t = 40/60ns MIN (5V/3V), t = 20/30ns MIN (5V/3V) 6 7 8 POLARITY PIN LOGIC HIGH SYNC (I/P) t t t 11 3 11 t 3 SCLK (I/P) 1 16 1 16 t 5 t 14 t 7 t t 6 12 t 6 t 8 DIN (I/O) DB15 DB0 DB15 DB0 THREE-STATE DATA WRITE DATA READ DIN BECOMES AN OUTPUT DIN BECOMES AN INPUT Figure 31. Timing Diagram for Read/Write Operation with DIN as an Input/Output (i.e., Mode 1) t = 75/115ns MAX (5V/3V), t = 40/60ns MIN (5V/3V), t = 20/30ns MIN (5V/3V), 6 7 8 t = 90/130ns MAX (5V/3V), t = 50/90ns MIN (5V/3V) 13 14 POLARITY PIN LOGIC HIGH 1 16 1 6 16 SCLK (I/P) t 14 t 7 t 6 t t t 13 6 8 DIN (I/O) DB15 DB0 DB15 DB0 DATA WRITE DATA READ DIN BECOMES AN INPUT Figure 32. Timing Diagram for Read/Write Operation with DIN as an Input/Output and SYNC Input Tied Low (i.e., Interface Mode 1) –24– REV. B AD7858/AD7858L Mode 2 (3-Wire SPI/QSPI Interface Mode) SYNC going low disables the three-state on the DOUT pin. This is the DEFAULT INTERFACE MODE. The first falling edge of the SCLK after the SYNC going low clocks out the first leading zero on the DOUT pin. The DOUT In Figure 33 below we have the timing diagram for interface pin is three-stated again a time t after the SYNC goes high. 12 Mode 2 which is the SPI/QSPI interface mode. Here the SYNC With the DIN pin the data input has to be set up a time t be- 7 input is active low and may be pulsed or tied permanently low. fore the SCLK rising edge as the part samples the input data on If SYNC is permanently low, 16 clock pulses must be applied to the SCLK rising edge in this case. If resetting the interface is the SCLK pin for the part to operate correctly, otherwise with a required, the SYNC must be taken high and then low. pulsed SYNC input a continuous SCLK may be applied pro- vided SYNC is low for only 16 SCLK cycles. In Figure 33 the t = –0.4t MIN (NONCONTINUOUS SCLK) �0.4t ns MIN/MAX (CONTINUOUS SCLK), 3 SCLK SCLK t = 75/115ns MAX (5V/3V), t = 40/60ns MIN (5V/3V), t = 20/30ns MIN (5V/3V), 6 7 8 POLARITY PIN LOGIC HIGH t = 30/50ns MIN (NONCONTINUOUS SCLK) (5V/3V), (30/50)/0.4t ns MIN/MAX 11 SCLK (CONTINUOUS SCLK) (5V/3V) SYNC (I/P) t 11 t t 3 9 SCLK (I/P) 1 2 3 4 5 6 16 t t 10 5 t 12 t 6 t 6 THREE-STATE THREE-STATE DOUT (O/P) DB15 DB14 DB13 DB12 DB11 DB10 DB0 t 7 t 8 t 8 DIN (I/P) DB15 DB14 DB13 DB12 DB11 DB10 DB0 Figure 33. SPI/QSPI Mode 2 Timing Diagram for Read/Write Operation with DIN Input, DOUT Output, and SYNC Input REV. B –25– AD7858/AD7858L CONFIGURING THE AD7858/AD7858L than one conversion. The options of using a hardware (pulsing The AD7858/AD7858L contains 14 on-chip registers which can the CONVST pin) or software (setting the CONVST bit to 1) be accessed via the serial interface. In the majority of applications it conversion start, and reading/writing during or after conversion will not be necessary to access all of these registers. Here the are shown in Figures 34 and 35. If the CONVST pin is never CLKIN signal is applied directly after power-on; the CLKIN used then it should be tied to DV permanently. Where refer- DD signal must be present to allow the part to perform a calibration. ence is made to the BUSY bit equal to a Logic 0, to indicate the This automatic calibration will be completed approximately 32 ms end of conversion, the user in this case would poll the BUSY bit after the AD7858 has powered up (4 MHz CLK). in the status register. For accessing the on-chip registers it is necessary to write to the Interface Mode 1 Configuration part. To change the channel from the default channel setting Figure 34 shows the flowchart for configuring the part in Inter- the user will be required to write to the part. To enable Serial face Mode 1. This mode of operation can only be enabled by Interface Mode 1 the user must also write to the part. Figure 34 writing to the control register and setting the 2/3 MODE bit. and 35 outline flowcharts of how to configure the AD7858/ Reading and writing cannot take place simultaneously in this AD7858L Serial Interface Modes 1 and 2 respectively. The mode as the DIN pin is used for both reading and writing. continuous loops on all diagrams indicate the sequence for more START POWER-ON, APPLY CLKIN SIGNAL, WAIT FOR AUTOMATIC CALIBRATION SERIAL INTERFACE MODE ? 1 INITIATE YES CONVERSION IN SOFTWARE ? NO APPLY SYNC (IF REQUIRED), SCLK, WRITE APPLY SYNC (IF REQUIRED), SCLK, TO CONTROL REGISTER SETTING CHANNEL WRITE TO CONTROL REGISTER SETTING CHANNEL AND TWO-WIRE MODE TWO-WIRE MODE WRITE TO CONTROL REGISTER SETTING CONVST PULSE CONVST PIN BIT TO 1 (SEE NOTE) READ DATA YES DURING CONVERSION ? WAIT APPROX. 200ns AFTER NO CONVST RISING EDGE OR AFTER END OF CONTROL REGISTER WRITE WAIT FOR BUSY SIGNAL TO GO LOW OR WAIT FOR BUSY BIT = 0 APPLY SYNC (IF REQUIRED), SCLK, READ PREVIOUS CONVERSION RESULT ON DIN PIN APPLY SYNC (IF REQUIRED), SCLK, READ CURRENT CONVERSION RESULT ON DIN PIN NOTE: TWO SEPARATE WRITES ARE REQUIRED TO SET A NEW CHANNEL ADDRESS AND INITIATE A CONVERSION ON THAT NEW CHANNEL IN SOFTWARE AS THE ACQUISITION TIME (2 t ) CLKIN MUST ELAPSE BEFORE THE CONVERSION BEGINS. IF BOTH COMMANDS ARE ISSUED IN THE ONE WRITE THE RESULT OF THIS CONVERSION SHOULD BE DISCARDED AND THE NEXT CONVERSION ON THAT SAME CHANNEL WILL PROVIDE CORRECT RESULTS. Figure 34. Flowchart for Setting Up, Reading, and Writing in Interface Mode 1 –26– REV. B AD7858/AD7858L Interface Mode 2 Configuration that no valid data is written to any of the registers. When using Figure 35 shows the flowchart for configuring the part in Inter- the software conversion start and transferring data during con- face Mode 2. In this case the read and write operations take version Note 1 must be obeyed. place simultaneously via the serial port. Writing all 0s ensures START POWER-ON, APPLY CLKIN SIGNAL, WAIT FOR AUTOMATIC CALIBRATION SERIAL INTERFACE MODE ? 2 INITIATE CONVERSION YES IN SOFTWARE ? NO TRANSFER YES DATA DURING CONVERSION ? PULSE CONVST PIN APPLY SYNC (IF REQUIRED), SCLK, WRITE TO CONTROL REGISTER SETTING CHANNEL, (SEE NOTE 1) NO WRITE TO CONTROL REGISTER APPLY SYNC (IF REQUIRED), SCLK, WRITE TRANSFER SETTING CONVST BIT TO 1, YES TO CONTROL REGISTER SETTING CHANNEL DATA DURING READ PREVIOUS RESULT ON CONVERSION DOUT PIN (SEE NOTES 1&2) ? WRITE TO CONTROL REGISTER SETTING CONVST BIT TO 1, READ WAIT APPROX 200ns AFTER NO CURRENT CONVERSION RESULT CONVST RISING EDGE ON DOUT PIN (SEE NOTE 2) WAIT FOR BUSY SIGNAL TO GO LOW OR WAIT FOR BUSY BIT = 0 WAIT FOR BUSY SIGNAL TO GO LOW APPLY SYNC (IF REQUIRED), SCLK, READ OR PREVIOUS CONVERSION RESULT ON DOUT WAIT FOR BUSY BIT = 0 PIN, AND WRITE CHANNEL SELECTION APPLY SYNC (IF REQUIRED), SCLK, READ CURRENT CONVERSION RESULT ON DOUT PIN, AND WRITE CHANNEL SELECTION NOTES 1 WHEN USING THE SOFTWARE CONVERSION START AND TRANSFERRING DATA DURING CONVERSION THE USER MUST ENSURE THE CONTROL REGISTER WRITE OPERATION EXTENDS BEYOND THE FALLING EDGE OF BUSY. THE FALLING EDGE OF BUSY RESETS THE CONVST BIT TO 0 AND ONLY AFTER THIS TIME CAN IT BE REPROGRAMMED TO 1 TO START THE NEXT CONVERSION. 2 TWO SEPARATE WRITES ARE REQUIRED TO SET A NEW CHANNEL ADDRESS AND INITIATE A CONVERSION ON THAT NEW CHANNEL IN SOFTWARE AS THE ACQUISITION TIME (2 t ) MUST ELAPSE BEFORE THE CONVERSION BEGINS. IF BOTH COMMANDS ARE ISSUED IN THE ONE WRITE THE CLKIN RESULT OF THIS CONVERSION SHOULD BE DISCARDED AND THE NEXT CONVERSION ON THAT SAME CHANNEL WILL PROVIDE CORRECT RESULTS. Figure 35. Flowchart for Setting Up, Reading, and Writing in Interface Mode 2 REV. B –27– AD7858/AD7858L OPTIONAL MICROPROCESSOR INTERFACING AD7858/AD7858L In many applications, the user may not require the facility of 4MHz/1.8MHz CONVST 8XC51/L51 writing to most of the on-chip registers. The only writing neces- sary is to set the input channel configuration. After this the MASTER CLKIN CONVST is applied, a conversion is performed, and the result P3.1 SCLK SLAVE may be read using the SCLK to clock out the data from the P3.0 DIN output register on to the DOUT pin. At the same time a write (INT0/P3.2) BUSY operation occurs and this may consist of all 0s where no data is OPTIONAL written to the part or may set a different input channel configu- SYNC ration for the next conversion. The SCLK may be connected to the CLKIN pin if the user does not want to have to provide Figure 37. 8XC51/PIC16C42 Interface separate serial and master clocks. With this arrangement the SYNC signal must be low for 16 SCLK cycles for the read and AD7858/AD7858L to 68HC11/16/L11/PIC16C42 Interface write operations. Figure 38 shows the AD7858/AD7858L SPI/QSPI interface to the 68HC11/16/L11/PIC16C42. The 68L11 is for interfacing to the AD7858/AD7858L when the supply is 3 V. The AD7858/ CONVST CONVERSION START AD7858L is in Interface Mode 2. The SYNC line is not used 4MHz/1.8MHz CLKIN and is tied to DGND. The µController is configured as the mas- MASTER CLOCK SCLK ter, by setting the MSTR bit in the SPCR to 1, and provides the SYNC SIGNAL TO AD7858/ serial clock on the SCK pin. For all the µControllers the CPOL GATE THE SCLK SYNC AD7858L bit is set to 1 and for the 68HC11/16/L11 the CPHA bit is set to DIN SERIAL DATA INPUT 1. The CLKIN and CONVST signals can be supplied from the SERIAL DATA DOUT OUTPUT µController or from separate sources. The BUSY signal can be used as an interrupt to tell the µController when the conversion is finished, then the reading and writing can take place. If re- Figure 36. Simplified Interface Diagram quired the reading and writing can take place during conversion AD7858/AD7858L to 8XC51 Interface and there will be no need for the BUSY signal in this case. Figure 37 shows the AD7858/AD7858L interface to the 8XC51. The 8XL51 is for interfacing to the AD7858/AD7858L OPTIONAL AD7858/AD7858L when the supply is at 3 V. The 8XC51 only runs at 5 V. The 4MHz/1.8MHz CONVST 8XC51 is in Mode 0 operation. This is a two-wire interface DV DD consisting of the SCLK and the DIN which acts as a bidirec- 68HC11/L11/16 CLKIN SPI tional line. The SYNC is tied low. The BUSY line can be used SS SYNC SLAVE HC16, QSPI to give an interrupt driven system but this would not normally SCK SCLK MASTER be the case with the 8XC51. For the 8XC51 12 MHz version MISO DOUT the serial clock will run at a maximum of 1 MHz so the serial OPTIONAL IRQ BUSY interface of the AD7858/AD7858L will only be running at MOSI DIN 1 MHz. The CLKIN signal must be provided separately to the AD7858/AD7858L from a port line on the 8XC51 or from a source other than the 8XC51. Here the SCLK cannot be tied to Figure 38. 68HC11 and 68HC16 Interface the CLKIN as the SYNC is tied low permanently. The CONVST For the 68HC16 the word length should be set to 16 bits, and signal can be provided from an external timer or conversion can the SS line should be tied to the SYNC pin for the QSPI inter- be started in software if required. The sequence of events would face. The micro-sequencer and RAM associated with the typically be to write to the control register via the DIN line setting 68HC16 QSPI port can be used to perform a number of read a conversion start and the 2-wire interface mode (this would be and write operations, and store the conversion results in performed in two 8-bit writes), wait for the conversion to be memory, independent of the CPU. This is especially useful when finished (4.6 µs with 4 MHz CLKIN), read the conversion result reading the conversion results from all eight channels consecu- data on the DIN line (this would be performed in two 8-bits tively. The command section of the QSPI port RAM would be reads), and repeat the sequence. The maximum serial frequency programmed to perform a conversion on one channel, read the will be determined by the data access and hold times of the conversion result, perform a conversion on the next channel, 8XC51 and the AD7858/AD7858L. read the conversion result, and so on until all eight conversion results are stored into the QSPI RAM. –28– REV. B AD7858/AD7858L AD7858/AD7858L to DSP56000/1/2/L002 Interface A typical sequence of events would be to write to the control Figure 40 shows the AD7858/AD7858L to DSP56000/1/2/ register via the DIN line setting a conversion start and at the L002 interface. Here the DSP5600x is the master and the same time reading data from the previous conversion on the AD7858 is the slave. The AD7858/AD7858L is in Interface DOUT line (both the read and write operations would each be Mode 2. The DSP56L002 is used when the AD7858/AD7858L two 8-bit operations, one 16-bit operation for the 68HC16), is being operated at 3 V. The setting of the bits in the registers wait for the conversion to be finished (= 4.6 µs for AD7858 of the DSP5600x would be for synchronous operation (SYN = with 4 MHz CLKIN), and then repeat the sequence. The maxi- 1), internal frame sync (SCD2 = 1), gated internal clock (GCK mum serial frequency will be determined by the data access and = 1, SCKD = 1), 16-bit word length (WL1 = 1, WL0 = 0). Since hold times of the µControllers and the AD7858/AD7858L. a gated clock is used here the SCLK cannot be tied to the CLKIN AD7858/AD7858L to ADSP-21xx Interface of the AD7858/AD7858L. The SCLK from the DSP5600x Figure 39 shows the AD7858/AD7858L interface to the ADSP- must be inverted before it is applied to the AD7858/AD7858L. 21xx. The ADSP-21xx is the master and the AD7858/AD7858L Again the data access and hold times of the DSP5600x and is the slave. The AD7858/AD7858L is in Interface Mode 2. the AD7858/AD7858L allows for a SCLK of 4 MHz/1.8 MHz. For the ADSP-21xx the bits in the serial port control register should be set up as TFSR = RFSR = 1 (need a frame sync for OPTIONAL every transfer), SLEN = 15 (16-bit word length), TFSW = AD7858/AD7858L 4MHz/1.8MHz RFSW = 1 (alternate framing mode for transmit and receive CONVST operations), INVRFS = INVTFS = 1 (active low RFS and DSP56000/1/2/L002 CLKIN TFS), IRFS = 0, ITFS = 1 (External RFS and internal TFS), SCK SCLK SLAVE and ISCLK = 1 (internal serial clock). The CLKIN and SRD DOUT CONVST signals can be supplied from the ADSP-21xx or MASTER SC2 SYNC from an external source. The serial clock from the ADSP-21xx OPTIONAL IRQ BUSY must be inverted before the SCLK pin of the AD7858/AD7858L. STD DIN This SCLK could also be used to drive the CLKIN input of the AD7858/AD7858L. The BUSY signal indicates when the con- version is finished and may not be required. The data access Figure 40. DSP56000/1/2 Interface and hold times of the ADSP-21xx and the AD7858/AD7858L allow for a serial clock of 4 MHz/1.8 MHz at 5 V and 3.3 MHz/ 1.8 MHz at 3 V supplies. OPTIONAL AD7858/AD7858L CONVST ADSP-21xx 4MHz/1.8MHz CLKIN SCK SCLK DR DOUT SYNC RFS MASTER SLAVE TFS OPTIONAL IRQ BUSY DIN DT Figure 39. ADSP-21xx Interface REV. B –29– AD7858/AD7858L APPLICATION HINTS Good decoupling is also important. All analog supplies should Grounding and Layout be decoupled with 10 µF tantalum in parallel with 0.1 µF ca- The analog and digital supplies to the AD7858/AD7858L are pacitors to AGND. All digital supplies should have a 0.1 µF independent and separately pinned out to minimize coupling disc ceramic capacitor to AGND. To achieve the best from between the analog and digital sections of the device. The part these decoupling components, they must be placed as close as has very good immunity to noise on the power supplies as can possible to the device, ideally right up against the device. In be seen by the PSRR vs. Frequency graph. However, care systems where a common supply voltage is used to drive both should still be taken with regard to grounding and layout. the AV and DV of the AD7858/AD7858L, it is recom- DD DD mended that the system’s AV supply be used. In this case DD The printed circuit board that houses the AD7858/AD7858L there should be a 10 Ω resistor between the AV pin and DD should be designed such that the analog and digital sections are DV pin. This supply should have the recommended analog DD separated and confined to certain areas of the board. This facili- supply decoupling capacitors between the AV pin of the DD tates the use of ground planes that can be separated easily. A AD7858/AD7858L and AGND and the recommended digital minimum etch technique is generally best for ground planes as supply decoupling capacitor between the DV pin of the DD it gives the best shielding. Digital and analog ground planes AD7858/AD7858L and DGND. should only be joined in one place. If the AD7858/AD7858L is the only device requiring an AGND to DGND connection, Evaluating the AD7858/AD7858L Performance then the ground planes should be connected at the AGND and The recommended layout for the AD7858/AD7858L is out- DGND pins of the AD7858/AD7858L. If the AD7858/ lined in the evaluation board for the AD7858/AD7858L. The AD7858L is in a system where multiple devices require AGND evaluation board package includes a fully assembled and tested to DGND connections, the connection should still be made at evaluation board, documentation, and software for controlling one point only, a star ground point which should be established the board from the PC via the EVAL-CONTROL BOARD. as close as possible to the AD7858/AD7858L. The EVAL-CONTROL BOARD can be used in conjunction with the AD7858/AD7858L Evaluation board, as well as many Avoid running digital lines under the device as these will couple other Analog Devices evaluation boards ending in the CB desig- noise onto the die. The analog ground plane should be allowed nator, to demonstrate/evaluate the ac and dc performance of the to run under the AD7858/AD7858L to avoid noise coupling. AD7858/AD7858L. The power supply lines to the AD7858/AD7858L should use as large a trace as possible to provide low impedance paths and The software allows the user to perform ac (fast Fourier trans- reduce the effects of glitches on the power supply line. Fast form) and dc (histogram of codes) tests on the AD7858/ switching signals like clocks should be shielded with digital AD7858L. It also gives full access to all the AD7858/AD7858L ground to avoid radiating noise to other sections of the board, on-chip registers allowing for various calibration and power- and clock signals should never be run near the analog inputs. down options to be programmed. Avoid crossover of digital and analog signals. Traces on oppo- AD785x Family site sides of the board should run at right angles to each other. All parts are 12 bits, 200 kSPS, 3.0 V to 5.5 V. This will reduce the effects of feedthrough through the board. A AD7853 – Single Channel Serial microstrip technique is by far the best but is not always possible with a double-sided board. In this technique, the component AD7854 – Single Channel Parallel side of the board is dedicated to ground planes while signals are AD7858 – Eight Channel Serial placed on the solder side. AD7859 – Eight Channel Parallel –30– REV. B AD7858/AD7858L PAGE INDEX Topic Page No. FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Self-Calibration Description . . . . . . . . . . . . . . . . . . . . . . . 21 GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . 1 Self-Calibration Timing . . . . . . . . . . . . . . . . . . . . . . . . . . 21 PRODUCT HIGHLIGHTS . . . . . . . . . . . . . . . . . . . . . . . . . 1 System Calibration Description . . . . . . . . . . . . . . . . . . . . 21 SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 System Gain and Offset Interaction . . . . . . . . . . . . . . . . . 22 TIMING SPECIFICATIONS . . . . . . . . . . . . . . . . . . . . . . . 4 System Calibration Timing . . . . . . . . . . . . . . . . . . . . . . . 22 TYPICAL TIMING DIAGRAMS . . . . . . . . . . . . . . . . . . . . 5 SERIAL INTERFACE SUMMARY . . . . . . . . . . . . . . . . . . 23 ABSOLUTE MAXIMUM RATINGS . . . . . . . . . . . . . . . . . 6 Resetting The Serial Interface . . . . . . . . . . . . . . . . . . . . . 23 ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 DETAILED TIMING SECTION PIN CONFIGURATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Mode 1 (2-Wire 8051 Interface) . . . . . . . . . . . . . . . . . . . 24 PIN FUNCTION DESCRIPTIONS . . . . . . . . . . . . . . . . . . 7 Mode 2 (3-Wire SPI/QSPI Interface) . . . . . . . . . . . . . . . . 25 TERMINOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 CONFIGURING THE AD7858/AD7858L . . . . . . . . . . . . 26 ON-CHIP REGISTERS Interface Mode 1 Configuration . . . . . . . . . . . . . . . . . . . . 26 Addressing the On-Chip Registers . . . . . . . . . . . . . . . . . . . 9 Interface Mode 2 Configuration . . . . . . . . . . . . . . . . . . . . 27 CONTROL REGISTER . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 MICROPROCESSOR INTERFACING . . . . . . . . . . . . . . . 28 STATUS REGISTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 AD7858/AD7858L–8XC51 Interface . . . . . . . . . . . . . . . 28 CALIBRATION REGISTERS . . . . . . . . . . . . . . . . . . . . . . 13 AD7858/AD7858L–68HC11/16/L11/PIC16C42 Addressing the Calibration Registers . . . . . . . . . . . . . . . . 13 Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Writing to/Reading from the Calibration Registers . . . . . . 13 AD7858/AD7858L–ADSP-21xx Interface . . . . . . . . . . . . 29 Adjusting the Offset Calibration Registers . . . . . . . . . . . . 14 AD7858/AD7858L–DSP56000/1/2/L002 Interface . . . . . 29 Adjusting the Gain Calibration Register . . . . . . . . . . . . . . 14 APPLICATION HINTS CIRCUIT INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . 15 Grounding and Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 CONVERTER DETAILS . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Evaluating the AD7858/AD7858L Performance . . . . . . . 30 TYPICAL CONNECTION DIAGRAM . . . . . . . . . . . . . . 15 INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 ANALOG INPUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . 32 Acquisition Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 TABLE INDEX DC/AC Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 # Title Page No. Input Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Table I. Write Register Addressing . . . . . . . . . . . . . . . . . 9 Transfer Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Table II. Read Register Addressing . . . . . . . . . . . . . . . . . 9 REFERENCE SECTION . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Table III. Channel Selection . . . . . . . . . . . . . . . . . . . . . . 11 PERFORMANCE CURVES . . . . . . . . . . . . . . . . . . . . . . . . 18 Table IV. Calibration Selection . . . . . . . . . . . . . . . . . . . . 11 POWER-DOWN OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . 18 Table V. Calibration Register Addressing . . . . . . . . . . . 13 POWER-UP TIMES Table VI. Power Management Options . . . . . . . . . . . . . . 19 Using an External Reference . . . . . . . . . . . . . . . . . . . . . . 19 Table VII. Power Consumption vs. Throughput . . . . . . . 20 Using the Internal (On-Chip) Reference . . . . . . . . . . . . . 19 Table VIII. Calibration Times (AD7858 with 4 MHz POWER VS. THROUGHPUT RATE . . . . . . . . . . . . . . . . 20 CLKIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 CALIBRATION SECTION Table IX. SCLK Active Edges . . . . . . . . . . . . . . . . . . . . . 23 Calibration Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Table X. Interface Mode Description . . . . . . . . . . . . . . . 23 Automatic Calibration on Power-On . . . . . . . . . . . . . . . . 21 REV. B –31– AD7858/AD7858L OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 24-Lead Plastic DIP (N-24) 1.228 (31.19) 1.226 (31.14) 24 13 0.260 �0.001 (6.61 �0.03) 112 0.32 (8.128) 0.30 (7.62) PIN 1 0.130 (3.30) 0.128 (3.25) 15� 0.011 (0.28) 0 0.02 (0.5) 0.11 (2.79) 0.07 (1.78) SEATING 0.009 (0.23) PLANE 0.016 (0.41) 0.09 (2.28) 0.05 (1.27) NOTES 1. LEAD NO. 1 IDENTIFIED BY A DOT OR NOTCH. 2. PLASTIC LEADS WILL BE EITHER TIN PLATED OR SOLDER DIPPED IN ACCORDANCE WITH MIL-M-38510 REQUIREMENTS. 24-Lead Small Outline Package (R-24) 0.608 (15.45) 0.596 (15.13) 24 13 1 12 0.096 (2.44) PIN 1 0.03 (0.76) 0.089 (2.26) 0.02 (0.51) 6� 0.042 (1.067) 0.05 0.01 (0.254) 0.019 (0.49) 0� 0.018 (0.447) SEATING (1.27) 0.013 (0.32) 0.006 (0.15) 0.014 (0.35) PLANE BSC 0.009 (0.23) NOTES 1. LEAD NO. 1 IDENTIFIED BY A DOT. 2. SOIC LEADS WILL BE EITHER TIN PLATED OR SOLDER DIPPED IN ACCORDANCE WITH MIL-M-38510 REQUIREMENTS. 24-Lead Shrink Small Outline Package (RS-24) 0.328 (8.33) 0.318 (8.08) 24 13 1 12 0.07 (1.78) PIN 1 0.066 (1.67) 8� 0.037 (0.94) 0.0256 0.015 (0.38) 0� 0.008 (0.203) 0.022 (0.559) SEATING 0.009 (0.229) (0.65) 0.010 (0.25) 0.002 (0.050) PLANE BSC 0.005 (0.127) NOTES 1. LEAD NO. 1 IDENTIFIED BY A DOT. 2. LEADS WILL BE EITHER TIN PLATED OR SOLDER DIPPED IN ACCORDANCE WITH MIL-M-38510 REQUIREMENTS. –32– REV. B 0.311 (7.9) 0.301 (7.64) 0.212 (5.38) 0.299 (7.6) 0.205 (5.207) 0.291 (7.39) 0.414 (10.52) 0.398 (10.10) PRINTED IN U.S.A. C01337–0–6/00