ANALOG DEVICES AD8290

G = 50, CMOS Sensor Amplifier with Current Excitation AD8290 FEATURES GENERAL DESCRIPTION Supply voltage range: 2.6 V to 5.5 V The AD8290 contains both an adjustable current source to Low power drive a sensor and a difference amplifier to amplify the signal 1.2 mA + 2× excitation current voltage. The amplifier is set for a fixed gain of 50. The AD8290 0.5 μA shutdown current is an excellent solution for both the drive and the sensing aspects Low input bias current: ±100 pA required for pressure, temperature, and strain gage bridges. High CMRR: 120 dB In addition, because the AD8290 operates with low power, Space savings: 16-lead, 3.0 mm × 3.0 mm × 0.55 mm LFCSP works with a range of low supply voltages, and is available in a Excitation current low profile package, it is suitable for drive/sense circuits in 300 μA to 1300 μA range portable electronics as well. Set with external resistor The AD8290 is available in a lead free 3.0 mm × 3.0 mm × 0.55 mm package and is operational over the industrial APPLICATIONS temperature range of −40°C to +85°C. Bridge and sensor drives Portable electronics FUNCTIONAL BLOCK DIAGRAM C FILTER ENBL R SET 11 6 5 3 V CC 2 13 10 GND 15 C BRIDGE 4 ADC ANTI- ALIASING 14 AD8290 FILTER V REF NC NC NC NC NC NC 1 7 8 9 12 16 Figure 1. Rev. B Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. No Tel: 781.329.4700 www.analog.com license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Fax: 781.461.3113 ©2007–2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. 06745-001 AD8290 TABLE OF CONTENTS Features .............................................................................................. 1 Current Source............................................................................ 15 Applications....................................................................................... 1 Applications Information .............................................................. 16 General Description ......................................................................... 1 Typical Connections .................................................................. 16 Functional Block Diagram .............................................................. 1 Current Excitation...................................................................... 16 Revision History ............................................................................... 2 Enable/Disable Function........................................................... 16 Specifications..................................................................................... 3 Output Filtering.......................................................................... 16 Absolute Maximum Ratings............................................................ 5 Clock Feedthrough..................................................................... 16 Thermal Resistance ...................................................................... 5 Maximizing Performance Through Proper Layout............... 17 ESD Caution.................................................................................. 5 Power Supply Bypassing............................................................ 17 Pin Configuration and Function Descriptions............................. 6 Dual-Supply Operation ............................................................. 17 Typical Performance Characteristics ............................................. 7 Pressure Sensor Bridge Application......................................... 18 Theory of Operation ...................................................................... 14 Temperature Sensor Application.............................................. 19 Amplifier...................................................................................... 14 ADC/Microcontroller................................................................ 19 High Power Supply Rejection (PSR) and Common-Mode Outline Dimensions ....................................................................... 20 Rejection (CMR) ........................................................................ 14 Ordering Guide .......................................................................... 20 1/f Noise Correction .................................................................. 14 REVISION HISTORY 2/08—Rev. SpA to Rev. B Changes to Features Section............................................................ 1 Changes to Amplifier Section and Figure 43 .............................. 14 Changes to Current Source Section ............................................. 15 Changes to Current Excitation Section, Output Filtering Section, Clock Feedthrough Section, and Figure 45.................. 16 Changes to Figure 46...................................................................... 17 8/07—Revision SpA 7/07—Revision 0: Initial Version Rev. B | Page 2 of 20 AD8290 SPECIFICATIONS VCC = 2.6 V to 5.0 V, TA = 25°C, CFILTER = 6.8 nF, output antialiasing capacitor = 68 nF, RSET = 3 kΩ, common-mode input = 0.6 V, unless otherwise noted. Table 1. Parameter Test Conditions Min Typ Max Unit COMMON-MODE REJECTION RATIO (CMRR) Input voltage (VINP − VINN) range of 0.2 V to V − 1.7 V CC CMRR DC 110 120 dB NOISE Amplifier and VREF Input referred, f = 0.1 Hz to 10 Hz 0.75 μV p-p VOLTAGE OFFSET Output Offset Reference is internal and set to 865 900 935 mV 900 mV nominal Output Offset TC −40°C < T < +85°C −300 ±50 +300 μV/°C A PSR 120 dB INPUT CURRENT Input Bias Current −1000 ±100 +1000 pA Input Offset Current −2000 ±200 +2000 pA DYNAMIC RESPONSE Small Signal Bandwidth –3 dB With external filter capacitors, 0.25 kHz C = 6.8 nF and output FILTER antialiasing capacitor = 68 nF GAIN Gain 50 V/V Gain Error −1.0 ±0.5 +1.0 % Gain Nonlinearity ±0.0075 % Gain Drift −40°C < T < +85°C −25 ±15 +25 ppm/°C A INPUT Differential Input Impedance 50||1 MΩ||pF Input Voltage Range 0.2 V − 1.7 V CC OUTPUT Output Voltage Range VOUT = Gain × (VINP − VINN) + 0.075 VCC − 0.075 V Output Offset Output Series Resistance 10 ± 20% kΩ CURRENT EXCITATION Excitation Current Range Excitation current = 0.9 V/RSET 300 1300 μA Excitation Current Accuracy −1.0 +1.0 % Excitation Current Drift −40°C < TA < +85°C −250 ±50 +250 ppm/°C External Resistor for Setting 692 3000 Ω Excitation Current (RSET) Excitation Current Power −2.0 +0.2 +2.0 μA/V Supply Rejection Excitation Current Pin Voltage 0 V − 1.0 V CC Excitation Current Output Resistance 100 MΩ Required Capacitor from Ground to 0.1 μF Excitation Current Pin (CBRIDGE) ENABLE ENBL High Level V < 2.9 V V − 0.5 V V CC CC CC V > 2.9 V 2.4 V V CC CC ENBL Low Level GND 0.8 V Start-Up Time for ENBL 5.0 ms Rev. B | Page 3 of 20 AD8290 Parameter Test Conditions Min Typ Max Unit POWER SUPPLY Operating Range 2.6 5.5 V Quiescent Current 1.2 + 2× 1.8 + 2× mA excitation current excitation current Shutdown Current 0.5 10 μA TEMPERATURE RANGE For Operational Performance −40 +85 °C Rev. B | Page 4 of 20 AD8290 ABSOLUTE MAXIMUM RATINGS Stresses above those listed under Absolute Maximum Ratings Table 2. may cause permanent damage to the device. This is a stress Parameter Rating rating only; functional operation of the device at these or any Supply Voltage 6 V other conditions above those indicated in the operational Input Voltage +VSUPPLY section of this specification is not implied. Exposure to absolute 1 Differential Input Voltage ±VSUPPLY maximum rating conditions for extended periods may affect Output Short-Circuit Duration to GND Indefinite device reliability. Storage Temperature Range −65°C to +150°C Operating Temperature Range −40°C to +85°C THERMAL RESISTANCE Junction Temperature Range −65°C to +150°C θ is specified for the worst-case conditions, that is, a device JA Lead Temperature (Soldering, 10 sec) 300°C soldered in a circuit board for surface-mount packages. 1 Differential input voltage is limited to ±5.0 V, the supply voltage, or Table 3. whichever is less. Package Type θ θ Unit JA JC 16-Lead LFCSP (0.55 mm) 42.5 7.7 °C/W ESD CAUTION Rev. B | Page 5 of 20 AD8290 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS NC 1 12 NC AD8290 VCC 2 11 RSET TOP ENBL 3 VIEW 10 GND (Not to Scale) NC VOUT 4 9 NC = NO CONNECT Figure 2. Pin Configuration Table 4. Pin Function Descriptions Pin No. Mnemonic Description 1 1 NC Tie to Ground or Pin 16. 2 VCC Positive Power Supply Voltage. 3 ENBL Logic 1 enables the part, and Logic 0 disables the part. 4 VOUT Open End of Internal 10 kΩ Resistor. Tie one end of external antialiasing filter capacitor (6.8 nF) to this pin, and tie 1 the other end to ground. 5 CF2 Tie one end of the CFILTER (68 nF) that is in parallel with the internal gain resistor to this pin. 6 CF1 Tie the other end of the CFILTER (68 nF) that is in parallel with the internal gain resistor to this pin. 1 7 NC Tie to Ground. 1 8 NC Tie to Ground. 1 9 NC Tie to Ground. 1 10 GND Ground or Negative Power Supply Voltage. 11 RSET Tie one end of Resistor RSET to this pin to set the excitation current and tie the other end of Resistor RSET to Pin 10. 1 12 NC Tie to Ground. 1 13 IOUT Excitation Current Output. Tie one end of C (0.1 μF) to this pin and tie the other end of C to ground. BRIDGE BRIDGE 14 VINN Negative Input Terminal. 15 VINP Positive Input Terminal. 1 16 NC Tie to Ground or Pin 1. 17/Pad NC Pad should be floating and not tied to any potential. 1 During dual-supply operation, ground becomes the negative power supply voltage. Rev. B | Page 6 of 20 CF2 NC CF1 VINP NC VINN NC IOUT 06745-002 5 16 6 15 7 14 8 13 AD8290 TYPICAL PERFORMANCE CHARACTERISTICS 35 25 30 20 25 15 20 15 10 10 5 5 0 0 892 894 896 898 900 902 904 906 908 0.2988 0.2994 0.3000 0.3006 0.3012 0.2991 0.2997 0.3003 0.3009 OUTPUT VOLTAGE (mV) EXCITATION CURRENT (mA) Figure 3. Output Offset Voltage at 2.6 V Supply Figure 6. Excitation Output Current for 3 kΩ RSET at 2.6 V Supply 35 25 30 20 25 15 20 15 10 10 5 5 0 0 892 894 896 898 900 902 904 906 908 0.2988 0.2994 0.3000 0.3006 0.3012 0.2991 0.2997 0.3003 0.3009 OUTPUT VOLTAGE (mV) EXCITATION CURRENT (mA) Figure 4. Output Offset Voltage at 3.6 V Supply Figure 7. Excitation Output Current for 3 kΩ R at 3.6 V Supply SET 35 25 30 20 25 15 20 15 10 10 5 5 0 0 892 894 896 898 900 902 904 906 908 0.2988 0.2994 0.3000 0.3006 0.3012 0.2991 0.2997 0.3003 0.3009 OUTPUT VOLTAGE (mV) EXCITATION CURRENT (mA) Figure 5. Output Offset Voltage at 5.0 V Supply Figure 8. Excitation Output Current for 3 kΩ RSET at 5.0 V Supply Rev. B | Page 7 of 20 UNITS (%) UNITS (%) UNITS (%) 06745-005 06745-004 06745-003 UNITS (%) UNITS (%) UNITS (%) 06745-007 06745-008 06745-006 AD8290 25 25 20 20 15 15 10 10 5 5 0 0 1.296 1.297 1.298 1.299 1.300 1.301 1.302 1.303 1.304 1.305 –0.60 –0.56 –0.52 –0.48 –0.44 –0.40 –0.36 –0.32 –0.28 EXCITATION CURRENT (mA) GAIN ERROR (%) Figure 9. Output Excitation Current for 692 Ω R at 2.6 V Supply Figure 12. Percent Gain Error at 2.6 V Supply SET 25 25 20 20 15 15 10 10 5 5 0 0 1.296 1.297 1.298 1.299 1.300 1.301 1.302 1.303 1.304 1.305 –0.60 –0.56 –0.52 –0.48 –0.44 –0.40 –0.36 –0.32 –0.28 EXCITATION CURRENT (mA) GAIN ERROR (%) Figure 10. Output Excitation Current for 692 Ω R at 3.6 V Supply Figure 13. Percent Gain Error at 3.6 V Supply SET 25 25 20 20 15 15 10 10 5 5 0 0 1.296 1.297 1.298 1.299 1.300 1.301 1.302 1.303 1.304 1.305 –0.60 –0.56 –0.52 –0.48 –0.44 –0.40 –0.36 –0.32 –0.28 EXCITATION CURRENT (mA) GAIN ERROR (%) Figure 11. Output Excitation Current for 692 Ω RSET at 5.0 V Supply Figure 14. Percent Gain Error at 5.0 V Supply Rev. B | Page 8 of 20 UNITS (%) UNITS (%) UNITS (%) 06745-011 06745-010 06745-009 UNITS (%) UNITS (%) UNITS (%) 06745-014 06745-013 06745-012 AD8290 40 50 35 40 30 25 30 20 20 15 10 10 5 0 0 0.0030 0.0040 0.0050 0.0060 0.0070 –35 –15 5 2545 6585 105 125 0.0035 0.0045 0.0055 0.0065 DRIFT (µV/°C) NONLINEARITY (%) Figure 15. Percent Nonlinearity at 2.6 V Supply Figure 18. Output Offset Voltage Drift from −40°C to +85°C at 2.6 V Supply 35 50 30 40 25 30 20 15 20 10 10 5 0 0 –35 –15 5 2545 6585 105 125 0.0030 0.0040 0.0050 0.0060 0.0070 0.0035 0.0045 0.0055 0.0065 DRIFT (µV/°C) NONLINEARITY (%) Figure 19. Output Offset Voltage Drift from −40°C to +85°C at 3.6 V Supply Figure 16. Percent Nonlinearity at 3.6 V Supply 45 50 40 40 35 30 30 25 20 20 15 10 10 5 0 0 –35 –15 5 2545 6585 105 125 0.0030 0.0060 0.0090 0.0120 0.0150 0.0045 0.0075 0.0105 0.0135 DRIFT (µV/°C) NONLINEARITY (%) Figure 20. Output Offset Voltage Drift from −40°C to +85°C at 5.0 V Supply Figure 17. Percent Nonlinearity at 5.0 V Supply Rev. B | Page 9 of 20 UNITS (%) UNITS (%) UNITS (%) 06745-028 06745-027 06745-026 UNITS (%) UNITS (%) UNITS (%) 06745-033 06745-032 06745-031 AD8290 45 40 40 35 35 30 30 25 25 20 20 15 15 10 10 5 5 0 0 5 203550658095 110 125 10 20 30 40 50 60 70 80 90 DRIFT (ppm/°C) DRIFT (ppm/°C) Figure 21. Excitation Current Drift from −40°C to +85°C at Figure 24. Excitation Current Drift from −40°C to +85°C at 2.6 V Supply, RSET = 3 kΩ 2.6 V Supply, RSET = 692 Ω 45 40 40 35 35 30 30 25 25 20 20 15 15 10 10 5 5 0 0 10 20 30 40 50 60 70 80 90 5 203550658095 110 125 DRIFT (ppm/°C) DRIFT (ppm/°C) Figure 22. Excitation Current Drift from −40°C to +85°C at Figure 25. Excitation Current Drift from −40°C to +85°C at 3.6 V Supply, R = 3 kΩ 3.6 V Supply, R = 692 Ω SET SET 45 40 40 35 35 30 30 25 25 20 20 15 15 10 10 5 5 0 0 5 203550658095 110 125 10 20 30 40 50 60 70 80 90 DRIFT (ppm/°C) DRIFT (ppm/°C) Figure 23. Excitation Current Drift from −40°C to +85°C at Figure 26. Excitation Current Drift from −40°C to +85°C at 5.0 V Supply, RSET = 3 kΩ 5.0 V Supply, RSET = 692 Ω Rev. B | Page 10 of 20 UNITS (%) UNITS (%) UNITS (%) 06745-037 06745-036 06745-035 UNITS (%) UNITS (%) UNITS (%) 06745-041 06745-040 06745-039 AD8290 100 40 35 30 25 20 10 15 10 5 0 1 –16.0 –15.5 –15.0 –14.5 –14.0 –13.5 –13.0 –12.5 –12.0 1 10 100 1k 10k DRIFT (ppm/°C) FREQUENCY (Hz) Figure 27. Gain Drift from −40°C to +85°C at 2.6 V Supply Figure 30. Frequency Response for Supply Range of 2.6 V to 5.0 V (External CFILTER = 6.8 nF, Antialiasing Capacitor = 68 nF) 40 310 308 35 306 30 304 25 302 20 300 298 15 296 10 294 5 292 0 290 2.50 2.75 3.00 3.25 3.50 3.75 4.00 4.25 4.50 4.75 5.00 5.25 5.50 –16.0 –15.5 –15.0 –14.5 –14.0 –13.5 –13.0 –12.5 –12.0 POWER SUPPLY (V) DRIFT (ppm/°C) Figure 28. Gain Drift from −40°C to +85°C at 3.6 V Supply Figure 31. Low Excitation Current vs. Power Supply 40 1.310 1.308 35 1.306 30 1.304 25 1.302 20 1.300 1.298 15 1.296 10 1.294 5 1.292 0 1.290 2.50 2.75 3.00 3.25 3.50 3.75 4.00 4.25 4.50 4.75 5.00 5.25 5.50 –16.0 –15.5 –15.0 –14.5 –14.0 –13.5 –13.0 –12.5 –12.0 POWER SUPPLY (V) DRIFT (ppm/°C) Figure 32. High Excitation Current vs. Power Supply Figure 29. Gain Drift from −40°C to +85°C at 5.0 V Supply Rev. B | Page 11 of 20 UNITS (%) UNITS (%) UNITS (%) 06745-047 06745-046 06745-045 EXCITATION CURRENT (mA) EXCITATION CURRENT (µA) GAIN (V/V) 06745-019 06745-018 06745-020 AD8290 50.0 310 305 49.9 300 2.6V SUPPLY 49.8 295 2.6V SUPPLY 5V SUPPLY 3.6V SUPPLY 49.7 3.6V SUPPLY 290 5.0V SUPPLY 49.6 285 49.5 280 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 –55 –45 –35 –25 –15 –5 5 15 25 35 45 55 65 75 85 95 PIN VOLTAGE (V) TEMPERATURE (°C) Figure 33. Low Excitation Current vs. Excitation Current Pin Voltage Figure 36. Gain vs. Temperature 1.32 0.305 0.304 1.31 0.303 0.302 1.30 2.6V SUPPLY 5.0V SUPPLY 0.301 1.29 0.300 3.6V SUPPLY 2.6V SUPPLY 3.6V SUPPLY 0.299 1.28 0.298 5.0V SUPPLY 0.297 1.27 0.296 1.26 0.295 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 –45 –35 –25 –15 –5 5 15 25 35 45 55 65 75 85 95 PIN VOLTAGE (V) TEMPERATURE (°C) Figure 34. High Excitation Current vs. Excitation Current Pin Voltage Figure 37. Excitation Current vs. Temperature, R = 3 kΩ SET 0.905 1.315 0.904 1.310 0.903 2.6V SUPPLY 0.902 5.0V SUPPLY 1.305 0.901 3.6V SUPPLY 2.6V SUPPLY 0.900 1.300 3.6V SUPPLY 0.899 1.295 5.0V SUPPLY 0.898 0.897 1.290 0.896 1.285 0.895 –45 –35 –25 –15 –5 5 15 25 35 45 55 65 75 85 95 –45 –35 –25 –15 –5 5 15 25 35 45 55 65 75 85 95 TEMPERATURE (°C) TEMPERATURE (°C) Figure 35. Output Offset Voltage vs. Temperature Figure 38. Excitation Current vs. Temperature, R = 692 Ω SET Rev. B | Page 12 of 20 OUTPUT OFFSET (V) EXCITATION CURRENT (mA) EXCITATION CURRENT (µA) 06745-022 06745-021 06745-034 EXCITATION CURRENT (mA) EXCITATION CURRENT (mA) GAIN (V/V) 06745-042 06745-052 06745-038 AD8290 1.5 1000 1.4 5.0V SUPPLY 1.3 100 1.2 3.6V SUPPLY 1.1 1.0 2.6V SUPPLY 10 0.9 0.8 0.7 1 0.6 –45 –35 –25 –15 –5 5 15 25 35 45 55 65 75 85 95 0.01 0.1 1 10 100 1000 TEMPERATURE (°C) FREQUENCY (Hz) Figure 39. Quiescent Current vs. Temperature (Excludes 2× Excitation Current) Figure 41. Input-Referred Noise vs. Frequency 1.0 ENBL PIN 0.9 VOLTAGE (0V TO 5V) OUTPUT OFFSET 0.8 VOLTAGE 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 –0.1 –10 –5 0 5 10 15 20 TIME (10s/DIV) TIME (ms) Figure 40. 0.01 Hz to 10 Hz Input-Referred Noise Figure 42. ENBL Pin Voltage for 5.0 V Supply vs. Output Offset Voltage Start-Up Time Rev. B | Page 13 of 20 QUIESCENT CURRENT (mA) INPUT-REFERRED NOISE (100nV/DIV) 06745-049 06745-043 VOLTS (V) NOISE (nV Hz) 06745-050 06745-051 AD8290 THEORY OF OPERATION AMPLIFIER HIGH POWER SUPPLY REJECTION (PSR) AND COMMON-MODE REJECTION (CMR) The amplifier of the AD8290 is a precision current-mode correction instrumentation amplifier. It is internally set to a PSR and CMR indicate the amount that the offset voltage of an fixed gain of 50. The current-mode correction topology results amplifier changes when its common-mode input voltage or power in excellent accuracy. supply voltage changes. The autocorrection architecture of the AD8290 continuously corrects for offset errors, including those Figure 43 shows a simplified diagram illustrating the basic induced by changes in input or supply voltage, resulting in operation of the instrumentation amplifier within the AD8290 exceptional rejection performance. The continuous autocorrection (without correction). The circuit consists of a voltage-to-current provides great CMR and PSR performances over the entire amplifier (M1 to M6), followed by a current-to-voltage amplifier operating temperature range (−40°C to +85°C). (R2 and A1). Application of a differential input voltage forces a current through R1, resulting in a conversion of the input 1/f NOISE CORRECTION voltage to a signal current. Transistors M3 to M6 transfer twice Flicker noise, also known as 1/f noise, is noise inherent in the the signal current to the inverting input of the op amp, A1. A1 physics of semiconductor devices and decreases 10 dB per decade. and R2 form a current-to-voltage converter to produce a rail-to- The 1/f corner frequency of an amplifier is the frequency at which rail output voltage, VOUT. the flicker noise is equal to the broadband noise of the amplifier. At Op Amp A1 is a high precision auto-zero amplifier. This lower frequencies, flicker noise dominates causing large errors amplifier preserves the performance of the autocorrecting, in low frequency or dc applications. current-mode amplifier topology while offering the user a true Flicker noise appears as a slowly varying offset error that is voltage-in, voltage-out instrumentation amplifier. Offset errors reduced by the autocorrection topology of the AD8290, allowing are corrected internally. the AD8290 to have lower noise near dc than standard low An internal 0.9 V reference voltage is applied to the noninverting noise instrumentation amplifiers. input of A1 to set the output offset level. External Capacitor CFILTER is used to filter out correction noise. V CC C FILTER M5 M6 I R2 I R1 I – I R1 2I R1 I – I R1 R3 2R2 V – V I + I V = V + INP INN R1 OUT REF (V – V ) R1 INP INN I = R1 A1 R1 V BIAS VINP VINN M3 M4 M1 M2 V = 0.9V REF 2I 2I EXTERNAL Figure 43. Simplified Schematic of the Instrumentation Amplifier Within the AD8290 Rev. B | Page 14 of 20 06745-023 AD8290 CURRENT SOURCE PRECISION CURRENT The AD8290 generates an excitation current that is MIRROR programmable with an external resistor, RSET, as shown in Figure 44. A1 and M1 are configured to produce 0.9 V across R , which is based on an internal 0.9 V reference and creates a M1 SET A1 current equal to 0.9 V/R internal to the AD8290. This current SET V = 0.9V REF is passed to a precision current mirror and a replica of the current is sourced from the IOUT pin. This current can be used for the GND RSET IOUT excitation of a sensor bridge. CBRIDGE is used to filter noise from the current excitation circuit. R SET C BRIDGE SENSOR BRIDGE Figure 44. Current Excitation Rev. B | Page 15 of 20 06745-024 AD8290 APPLICATIONS INFORMATION For bandwidths greater than 10 Hz, an additional single-pole TYPICAL CONNECTIONS RC filter of 235 Hz is required on the output, which is also Figure 45 shows the typical connections for single-supply recommended when driving an ADC requiring an antialiasing operation when used with a sensor bridge. filter. Internal to the AD8290 is a series 10 kΩ resistor at the CURRENT EXCITATION output (R3 in Figure 43) and using an external 68 nF capacitor to ground produces an RC filter of 235 Hz on the output as well. In Figure 45, RSET is used to set the excitation current sourced at These two filters produce an overall bandwidth of approximately the IOUT pin. The formula for the excitation current I is OUT 160 Hz for the output signal. I = (900/R ) mA OUT SET In addition, when driving low impedances, the internal series where R is the resistor between Pin 10 (GND) and Pin 11 SET 10 kΩ resistor creates a voltage divider at the output. If it is (RSET). necessary to access the output of the internal amplifier prior The AD8290 is internally set by the factory to provide the to the 10 kΩ resistor, it is available at the CF2 pin. current excitation described by the previous formula (within the For applications with low bandwidths (<10 Hz), only the first tolerance range listed in Table 1). The range of RSET is 692 Ω to filter capacitor (C ) is required. In this case, the high FILTER 3 kΩ, resulting in a corresponding I of 1300 μA to 300 μA, OUT frequency noise from the auto-zero amplifier (output amplifier) respectively. is not filtered before the following stage. ENABLE/DISABLE FUNCTION CLOCK FEEDTHROUGH Pin 3 (ENBL) provides the enabling/disabling function of the The AD8290 uses two synchronized clocks to perform AD8290 to conserve power when the device is not needed. A autocorrection. The input voltage-to-current amplifiers Logic 1 turns the part on and allows it to operate normally. A are corrected at 60 kHz. Logic 0 disables the output and excitation current and reduces the quiescent current to less than 10 μA. Trace amounts of these clock frequencies can be observed at the output. The amount of feedthrough is dependent upon the The turn-on time upon switching Pin 3 high is dominated gain because the autocorrection noise has an input- and output- by the output filters. When the device is disabled, the output referred term. The correction feedthrough is also dependent becomes high impedance, enabling the muxing application of upon the values of the external capacitors, C2 and C . FILTER multiple AD8290 instrumentation amplifiers. OUTPUT FILTERING Filter Capacitor CFILTER is required to limit the amount of switching noise present at the output. The recommended bandwidth of the filter created by C and an internal FILTER 100 kΩ is 235 Hz. Select C based on FILTER C = 1/(235 × 2 × π × 100 kΩ) = 6.8 nF FILTER C FILTER 6.8nF 5.0V R SET 692Ω TO 3kΩ 11 6 5 3 RSET CF1 CF2 ENBL VCC 2 C1 0.1µF 13 IOUT AD8290 14 VINN GND 10 4 VOUT V 15 VINP OUT C2 68nF C BRIDGE NC NC NC NC NC NC 1 7 8 9 12 16 NC = NO CONNECT NOTES LAYOUT CONSIDERATIONS: 1. KEEP C1 CLOSE TO PIN 2 AND PIN 10. 2. KEEP R CLOSE TO PIN 11. SET Figure 45. Typical Single-Supply Connections Rev. B | Page 16 of 20 06745-025 AD8290 DUAL-SUPPLY OPERATION MAXIMIZING PERFORMANCE THROUGH PROPER LAYOUT The AD8290 can be configured to operate in dual-supply mode. An example of such a circuit is shown in Figure 46, where the To achieve the maximum performance of the AD8290, care AD8290 is powered by ±1.8 V supplies. When operating with should be taken in the circuit board layout. The PCB surface dual supplies, pins that are normally referenced to ground in the must remain clean and free of moisture to avoid leakage currents single-supply mode, now need to be referenced to the negative between adjacent traces. Surface coating of the circuit board supply. These pins include the following: Pin 1, Pin 7, Pin 8, Pin 9, reduces surface moisture and provides a humidity barrier, Pin 10, Pin 12, and Pin 16. External components, such as RSET, the reducing parasitic resistance on the board. sensing bridge, and the antialiasing filter capacitor at the output, R should be placed close to RSET (Pin 11) and GND (Pin 10). SET should also be referenced to the negative supply. Additionally, The paddle on the bottom of the package should not be connected two bypass capacitors should be added beyond what is necessary to any potential and should be floating. for single-supply operation: one between the negative supply For high impedance sources, the PCB traces from the AD8290 and ground, and the other between the positive and negative inputs should be kept to a minimum to reduce input bias supplies. current errors. When operating in dual-supply mode, the specifications change POWER SUPPLY BYPASSING and become relative to the negative supply. The input voltage range minimum shifts from 0.2 V to 0.2 V above the negative The AD8290 uses internally generated clock signals to perform supply (in this example: −1.6 V), the output voltage range shifts autocorrection. As a result, proper bypassing is necessary to from a minimum of 0.075 V to 0.075 V above the negative supply achieve optimum performance. Inadequate or improper bypassing (in this example: −1.725 V), and the excitation current pin of the supply lines can lead to excessive noise and offset voltage. voltage minimum shifts from 0 V to −1.8 V in this example. A 0.1 μF surface-mount capacitor should be connected between The maximum specifications of these three parameters are Pin 2 (VCC) and Pin 10 (GND) when operating with a single specified relative to V in Table 1 and do not change. CC supply and should be located as close as possible to those two pins. For other specifications, both the minimum and maximum specifications change. The output offset shifts from a minimum of +865 mV and maximum of +935 mV to a minimum of −935 mV and a maximum of −865 mV in the example. In addition, the logic levels for the ENBL operation should be adjusted accordingly. C FILTER 6.8nF 1.8V R SET C3 11 6 5 3 692Ω TO 3kΩ 0.1µF RSET CF1 CF2 ENBL –1.8V VCC 2 C1 0.1µF 13 IOUT –1.8V GND 10 AD8290 C5 14 VINN 0.1µF 15 VINP 4 V VOUT OUT C2 C BRIDGE NC NC NC NC NC NC 68nF 1 7 8 9 12 16 –1.8V –1.8V NC = NO CONNECT NOTES LAYOUT CONSIDERATIONS: 1. KEEP C1 CLOSE TO PIN 2 AND PIN 10. 2. KEEP C3 CLOSE TO PIN 2. 3. KEEP C5 CLOSE TO PIN 10. 4. KEEP R CLOSE TO PIN 11. SET Figure 46. Typical Dual-Supply Connections Rev. B | Page 17 of 20 06745-029 AD8290 The specifications for the bridge are show in Table 5 and the PRESSURE SENSOR BRIDGE APPLICATION chosen conditions for the AD8290 are listed in Table 6. Given its excitation current range, the AD8290 provides a good Given these specifications, calculations should be made to ensure match with pressure sensor circuits. Two such sensors are the Fujikura FGN-615PGSR and the Honeywell HPX050AS. Figure 47 that the AD8290 is operating within its required ranges. The shows the AD8290 paired with the Honeywell bridge and the combination of the excitation current and RP must be chosen appropriate connections. In this example, a resistor, R , is added to ensure that the conditions stay within the minimum and P to the circuit to ensure that the maximum output voltage of the maximum specifications of the AD8290. For this example, because the specifications of the HPX050AS are for a bridge AD8290 is not exceeded. Depending on the sensors specifications, excitation voltage of 3.0 V, care must be taken to scale the RP may not be necessary. resulting voltage calculations to the actual bridge voltage. The required calculations are shown in Table 7. C FILTER 6.8nF 3.3V R SET 2.7kΩ 11 6 5 3 RSET CF1 CF2 ENBL VCC 2 13 IOUT C1 R P C BRIDGE 8 0.1µF 2kΩ 0.1µF AD8290 10 HPX050AS GND 14 VINN 2 6 15 VINP 4 VOUT 4 5 C2 NC NC NC NC NC NC 68nF 1 7 8 9 12 16 NC = NO CONNECT Figure 47. HPX050AS Pressure Sensor Application Table 5. HPX050AS Specifications Bridge Impedance (Ω) Rated Offset (mV) Rated Output Span (mV) Minimum Maximum Minimum Maximum Minimum Maximum Bridge Excite Voltage (V) 4000 6000 −30 +30 0 80 3.0 Table 6. Typical AD8290 Conditions for Pressure Sensor Circuit AD8290 V (V) Excitation Current (μA) Parallel Resistor R (Ω) CC P 3.3 (2.6 to 5.5) 333.3 (300 to 1300) 2000 Table 7. Pressure Sensor Circuit Calculations Compared to AD8290 Minimum/Maximum Specifications Specification Calculation Unit Allowable Range of AD8290 Supply Current 1.867 mA Current Setting Resistor (R ) 2700 Ω 692 Ω to 3000 Ω SET Minimum Equivalent Resistance to IOUT Pin 1333 Ω Maximum Equivalent Resistance to IOUT Pin 1500 Ω Minimum Current into Bridge 83.333 μA Maximum Current into Bridge 111.111 μA Minimum Bridge Midpoint Voltage (Excluding Offset/Span) 0.222 V Maximum Bridge Midpoint Voltage (Excluding Offset/Span) 0.250 V Minimum Voltage at Current Output Pin (IOUT) 0.444 V >0.0 V Maximum Voltage at Current Output Pin (IOUT) 0.500 V <2.3 V Input Voltage Minimum 0.218 V >0.2 V Input Voltage Maximum 0.266 V <1.6 V Output Voltage Minimum 0.643 V >0.075 V Output Voltage Maximum 1.852 V <3.225 V Rev. B | Page 18 of 20 06745-030 AD8290 ADC/MICROCONTROLLER TEMPERATURE SENSOR APPLICATION In both of the previous applications, an ADC or a microcontroller The AD8290 can be used with a temperature sensor. Figure 48 can be used to follow the AD8290 to convert the output analog shows the AD8290 in conjunction with an RTD, in this signal to digital. For example, if there are multiple sensors in the example, a 2-wire PT100. The specifications for the sensor are system, the six channel ADuC814ARU microcontoller is an shown in Table 8 and the chosen conditions for the AD8290 are excellent candidate to interface with multiple AD8290s. listed in Table 9. Once again, care must be taken when picking the excitation current and RG such that the minimum and maximum specifications of the AD8290 are not exceeded. Sample calculations are shown in Table 10. C FILTER 6.8nF 3.3V R SET 3kΩ 11 6 5 3 RSET CF1 CF2 ENBL VCC 2 13 IOUT C1 C BRIDGE 0.1µF 0.1µF AD8290 GND 10 15 VINP RTD 14 VINN 4 VOUT R G 698Ω C2 NC NC NC NC NC NC 68nF 1 7 8 9 12 16 NC = NO CONNECT Figure 48. PT100 Temperature Sensor Application Connections Table 8. PT100 Specifications RTD Minimum @ 0°C RTD Maximum @ 100°C 100 Ω 138.5 Ω Table 9. Typical AD8290 Conditions for Temperature Sensor Circuit AD8290 V (V) Excitation Current (μA) Resistor from RTD to GND, R (Ω) CC G 3.30 (2.6 to 5.5) 300 (300 to 1300) 698 Table 10. Temperature Sensor Circuit Calculations Compared to AD8290 Minimum/Maximum Specifications Specification Calculation Unit Allowable Range of AD8290 Supply Current 1.8 mA Current Setting Resistor (RSET) 3000 Ω 692 Ω to 3000 Ω Minimum Equivalent Resistance to IOUT Pin 798 Ω Maximum Equivalent Resistance to IOUT Pin 836.5 Ω Minimum Voltage @ Current Output Pin (IOUT) 0.239 V >0.0 V Maximum Voltage @ Current Output Pin (IOUT) 0.251 V <2.3 V Input Voltage Minimum 0.209 V >0.2 V Input Voltage Maximum 0.251 V <1.6 V Output Voltage Minimum 2.365 V >0.075 V Output Voltage Maximum 3.013 V <3.225 V Rev. B | Page 19 of 20 06745-044 AD8290 OUTLINE DIMENSIONS 3.00 INDEX BSC SQ AREA 13 16 1 12 1.80 EXPOSED PAD 1.70 SQ 1.55 9 4 0.50 8 5 BSC 0.40 MAX TOP VIEW BOTTOM VIEW 0.30 NOM 0.60 0.05 MAX 0.55 0.02 NOM 0.51 SEATING 0.30 0.08 REF PLANE 0.25 0.18 COMPLIANT TO JEDEC STANDARDS MO-248-UEED. Figure 49. 16-Lead Lead Frame Chip Scale Package [LFCSP_UQ] 3 mm × 3 mm Body, Ultra Thin Quad (CP-16-12) Dimensions shown in millimeters ORDERING GUIDE Model Temperature Range Package Description Package Option Branding 1 AD8290ACPZ-R2 −40°C to +85°C 16-Lead LFCSP_UQ CP-16-12 Y0J 1 AD8290ACPZ-R7 −40°C to +85°C 16-Lead LFCSP_UQ CP-16-12 Y0J 1 AD8290ACPZ-RL −40°C to +85°C 16-Lead LFCSP_UQ CP-16-12 Y0J 1 Z = RoHS Compliant Part. ©2007–2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06745-0-2/08(B) Rev. B | Page 20 of 20 PIN 1 INDICATOR 053106-B