MAX1619 19-1483; Rev 0; 4/99 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface ________________General Description ____________________________Features The MAX1619 is a precise digital thermometer that reports 'Two Channels Measure Both Remote and Local the temperature of both a remote sensor and its own Temperatures package. The remote sensor is a diode-connected transis- 'No Calibration Required tor—typically a low-cost, easily mounted 2N3904 NPN type—that replaces conventional thermistors or thermo- 'SMBus 2-Wire Serial Interface couples. Remote accuracy is ±3°C for multiple transistor 'Programmable Under/Overtemperature Alarms manufacturers, with no calibration needed. The remote channel can also measure the die temperature of other 'OVERT Output for Fan Control ICs, such as microprocessors, that contain an on-chip, diode-connected transistor.'Supports SMBus Alert Response The 2-wire serial interface accepts standard System'Supports Manufacturer and Device ID Codes ® Management Bus (SMBus ) Write Byte, Read Byte, Send 'Accuracy Byte, and Receive Byte commands to program the alarm ±2°C (+60°C to +100°C, local) thresholds and to read temperature data. The data format is 7 bits plus sign, with each bit corresponding to 1°C, in ±3°C (-40°C to +125°C, local) two’s complement format. Measurements can be done ±3°C (+60°C to +100°C, remote) automatically and autonomously, with the conversion rate '3µA (typ) Standby Supply Current programmed by the user or programmed to operate in a single-shot mode. The adjustable rate allows the user to'70µA (max) Supply Current in Auto-Convert Mode control the supply-current drain. '+3V to +5.5V Supply Range The MAX1619 is nearly identical to the popular MAX1617A, 'Write-Once Protection with the additional feature of an overtemperature alarm out- put (OVERT) that responds to the remote temperature; this 'Small 16-Pin QSOP Package is optimal for fan control. Ordering Information ________________________Applications PART TEMP. RANGE PIN-PACKAGE Desktop and Notebook Central Office Computers Telecom Equipment MAX1619MEE -55°C to +125°C 16 QSOP Smart Battery Packs Test and Measurement Typical Operating Circuit LAN Servers Multichip Modules Industrial Controls +3V TO +5.5V 0.1μF 200Ω ___________________Pin Configuration V STBY TOP VIEW CC 10k EACH V 1 16 N.C. CC MAX1619 GND 2 15 STBY DXP SMBCLK CLOCK DXP 3 14 SMBCLK DATA SMBDATA DXN 4 MAX1619 13 N.C. INTERRUPT DXN N.C. 5 12 SMBDATA ALERT 2N3904 2200pF TO μC FAN ADD1 6 11 ALERT OVERT CONTROL GND 7 10 ADD0 ADD0 ADD1 GND GND 8 9 OVERT QSOP SMBus is a registered trademark of Intel Corp. ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface ABSOLUTE MAXIMUM RATINGS V to GND..............................................................-0.3V to +6V Continuous Power Dissipation (T = +70°C) CC A DXP, ADD_ to GND ....................................-0.3V to (V + 0.3V) QSOP (derate 8.30mW/°C above +70°C).....................667mW CC DXN to GND ..........................................................-0.3V to +0.8V Operating Temperature Range .........................-55°C to +125°C SMBCLK, SMBDATA, ALERT, OVERT, Junction Temperature......................................................+150°C STBY to GND............................................................-0.3V to +6V Storage Temperature Range .............................-65°C to +150°C SMBDATA, ALERT, OVERT Current....................-1mA to +50mA Lead Temperature (soldering, 10sec) .............................+300°C DXN Current .......................................................................±1mA ESD Protection (all pins, Human Body Model) ..................2000V Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (V = +3.3V, T = 0°C to +85°C, configuration byte = XCh, unless otherwise noted.) CC A PARAMETER CONDITIONS MIN TYP MAX UNITS ADC AND POWER SUPPLY Temperature Resolution (Note 1) Monotonicity guaranteed 8 Bits T = +60°C to +100°C -2 2 A Initial Temperature Error, °C Local Diode (Note 2) T = 0°C to +85°C -3 3 A T = +60°C to +100°C -3 3 Temperature Error, Remote Diode R °C (Notes 2, 3) T = -55°C to +125°C (Note 4) -5 5 R T = +60°C to +100°C -2.5 2.5 Temperature Error, Local Diode A Including long-term drift °C (Notes 1, 2) T = 0°C to +85°C -3.5 3.5 A Supply Voltage Range 3.0 5.5 V Undervoltage Lockout Threshold V input, disables A/D conversion, rising edge 2.60 2.80 2.95 V CC Undervoltage Lockout Hysteresis 50 mV Power-On Reset Threshold V , falling edge 1.0 1.7 2.5 V CC POR Threshold Hysteresis 50 mV SMBus static 310 Logic inputs Standby Supply Current forced to V µA CC Hardware or software standby, or GND 5 SMBCLK at 10kHz Autoconvert mode, average 0.25 conv/sec 35 70 Average Operating Supply Current measured over 4sec. Logic µA inputs forced to V or GND. 2.0 conv/sec 120 180 CC Conversion Time From stop bit to conversion complete (both channels) 94 125 156 ms Conversion Rate Timing Error Auto-convert mode -25 25 % High level 80 100 120 Remote-Diode Source Current DXP forced to 1.5V µA Low level 810 12 DXN Source Voltage 0.7 V Address Pin Bias Current ADD0, ADD1; momentary upon power-on reset 160 µA 2 _______________________________________________________________________________________ MAX1619 MAX1619 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface ELECTRICAL CHARACTERISTICS (continued) (V = +3.3V, T = 0°C to +85°C, configuration byte = XCh, unless otherwise noted.) CC A PARAMETER CONDITIONS MIN TYP MAX UNITS SMBus INTERFACE Logic Input High Voltage STBY, SMBCLK, SMBDATA; V = 3V to 5.5V 2.2 V CC Logic Input Low Voltage STBY, SMBCLK, SMBDATA; V = 3V to 5.5V 0.8 V CC Logic Output Low Sink Current 6 mA ALERT, OVERT, SMBDATA forced to 0.4V ALERT, OVERT Output High ALERT, OVERT, forced to 5.5V 1 µA Leakage Current Logic Input Current Logic inputs forced to V or GND -1 1 µA CC SMBus Input Capacitance SMBCLK, SMBDATA 5 pF SMBus Clock Frequency (Note 5) DC 100 kHz SMBCLK Clock Low Time t , 10% to 10% points 4.7 µs LOW SMBCLK Clock High Time t , 90% to 90% points 4 µs HIGH SMBus Start-Condition Setup Time 4.7 µs SMBus Repeated Start-Condition t , 90% to 90% points 500 ns SU:STA Setup Time SMBus Start-Condition Hold Time t , 10% of SMBDATA to 90% of SMBCLK 4 µs HD:STA SMBus Stop-Condition Setup Time t , 90% of SMBCLK to 10% of SMBDATA 4 µs SU:STO SMBus Data Valid to SMBCLK t , 10% or 90% of SMBDATA to 10% of SMBCLK 250 ns SU:DAT Rising-Edge Time SMBus Data-Hold Time t (Note 6) 0 µs HD:DAT SMBCLK Falling Edge to SMBus Master clocking in data 1 µs Data-Valid Time ELECTRICAL CHARACTERISTICS (V = +3.3V, T = -55°C to +125°C, configuration byte = XCh, unless otherwise noted.) (Note 4) CC A PARAMETER CONDITIONS MIN TYP MAX UNITS ADC AND POWER SUPPLY Temperature Resolution (Note 1) Monotonicity guaranteed 8 Bits T = +60°C to +100°C -2 2 Initial Temperature Error, A °C Local Diode (Note 2) T = -55°C to +125°C -3 3 A T = +60°C to +100°C -3 3 R Temperature Error, Remote Diode °C (Notes 2, 3) T = -55°C to +125°C -5 5 R Supply Voltage Range 3.0 5.5 V Conversion Time From stop bit to conversion complete (both channels) 94 125 156 ms Conversion Rate Timing Error Autoconvert mode -25 25 % _______________________________________________________________________________________ 3 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface ELECTRICAL CHARACTERISTICS (continued) (V = +3.3V, T = -55°C to +125°C, configuration byte = XCh, unless otherwise noted.) (Note 4) CC A PARAMETER CONDITIONS MIN TYP MAX UNITS SMBus INTERFACE V = 3V 2.2 CC Logic Input High Voltage STBY, SMBCLK, SMBDATA V V = 5.5V 2.4 CC Logic Input Low Voltage STBY, SMBCLK, SMBDATA; V = 3V to 5.5V 0.8 V CC Logic Output Low Sink Current ALERT, OVERT, SMBDATA forced to 0.4V 6 mA ALERT, OVERT Output High ALERT, OVERT forced to 5.5V 1 µA Leakage Current Logic Input Current Logic inputs forced to V or GND -2 2 µA CC Note 1: Guaranteed but not 100% tested. Note 2: Quantization error is not included in specifications for temperature accuracy. For example, if the MAX1619 device tempera- ture is exactly +66.7°C, the ADC may report +66°C, +67°C, or +68°C (due to the quantization error plus the +1/2°C offset used for rounding up) and still be within the guaranteed ±1°C error limits for the +60°C to +100°C temperature range (Table 2). Note 3: A remote diode is any diode-connected transistor from Table 1. T is the junction temperature of the remote diode. See R Remote Diode Selection for remote diode forward voltage requirements. Note 4: Specifications from -55°C to +125°C are guaranteed by design, not production tested. Note 5: The SMBus logic block is a static design that works with clock frequencies down to DC. While slow operation is possible, it violates the 10kHz minimum clock frequency and SMBus specifications, and may monopolize the bus. Note 6: Note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of SMBCLK’s falling edge. __________________________________________Typical Operating Characteristics (T = +25°C, unless otherwise noted.) A TEMPERATURE ERROR TEMPERATURE ERROR TEMPERATURE ERROR vs. vs. PC BOARD RESISTANCE vs. REMOTE-DIODE TEMPERATURE POWER-SUPPLY NOISE FREQUENCY 12 20 2 V = SQUARE WAVE APPLIED TO IN V WITH NO 0.1μF V CAPACITOR 15 CC CC V = 250mVp-p IN 9 10 1 REMOTE DIODE ZETEX FMMT3904 PATH = DXP TO GND 5 V = 100mVp-p IN LOCAL DIODE 6 0 0 MOTOROLA MMBT3904 -5 V = 100mVp-p IN REMOTE DIODE 3 -10 PATH = DXP TO V (5V) -1 CC RANDOM -15 SAMPLES 0 -20 -2 50 500 5k 50k 500k 5M 50M 1 10 100 -50 0 50 100 150 FREQUENCY (Hz) LEAKAGE RESISTANCE (MΩ) TEMPERATURE (°C) 4 _______________________________________________________________________________________ MAX1619 TEMPERATURE ERROR (°C) MAX1619-01 TEMPERATURE ERROR (°C) MAX1619-02 TEMPERATURE ERROR (°C) MAX1619-03 MAX1619 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface Typical Operating Characteristics (continued) (T = +25°C, unless otherwise noted.) A TEMPERATURE ERROR vs. TEMPERATURE ERROR vs. STANDBY SUPPLY CURRENT DXP–DXN CAPACITANCE vs. CLOCK FREQUENCY COMMON-MODE NOISE FREQUENCY 20 50 10 V = SQUARE WAVE IN V = 5V CC AC-COUPLED TO DXN 40 8 V = 100mVp-p IN 30 6 10 V = 5V CC 20 4 V = 50mVp-p IN V = 25mVp-p IN V = 3.3V CC 2 10 0 0 0 04 20060 80 100 1 10 100 1000 0.1 1 10 100 SMBCLK FREQUENCY (kHz) FREQUENCY (MHz) DXP–DXN CAPACITANCE (nF) OPERATING SUPPLY CURRENT STANDBY SUPPLY CURRENT INTERNAL DIODE vs. SUPPLY VOLTAGE vs. CONVERSION RATE RESPONSE TO THERMAL SHOCK 100 500 125 ADD0, ADD1 = GND V = 5V CC AVERAGED MEASUREMENTS 400 60 100 20 300 75 ADD0, ADD1 = HIGH-Z 200 6 50 3 100 25 16-QSOP IMMERSED IN +115°C FLUORINERT BATH 0 0 0 031425 01 0.0625 0.125 0.25 0.5 2 4 8 -2 04 26 8 10 CONVERSION RATE (Hz) SUPPLY VOLTAGE (V) TIME (sec) _______________________________________________________________________________________ 5 SUPPLY CURRENT (μA) TEMPERATURE ERROR (°C) MAX1619-04 MAX1619-09 TEMPERATURE ERROR (°C) SUPPLY CURRENT (μA) MAX1619-10 MAX1619-07 TEMPERATURE (°C) SUPPLY CURRENT (μA) MAX1619-11 MAX1619-08 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface Pin Description PIN NAME FUNCTION Supply Voltage Input, 3V to 5.5V. Bypass to GND with a 0.1µF capacitor. A 200Ω series resistor is recom- 1 V CC mended but not required for additional noise filtering. 2 GND Not internally connected. Connect to GND to act against leakage paths from V to DXP. CC Combined Current Source and A/D Positive Input for Remote-Diode Channel. Do not leave DXP floating; 3 DXP connect DXP to DXN if no remote diode is used. Place a 2200pF capacitor between DXP and DXN for noise filtering. Combined Current Sink and A/D Negative Input. DXN is normally internally biased to a diode voltage 4 DXN above ground. 5, 13, N.C. No Connection. Not internally connected. May be used for PC board trace routing. 16 SMBus Address Select Pin (Table 8). ADD0 and ADD1 are sampled upon power-up. Excess capacitance 6 ADD1 (>50pF) at the address pins when floating may cause address-recognition problems. 7, 8 GND Ground Overtemperature Alarm Output, Open Drain. This is an unlatched alarm output that responds only to the 9 OVERT remote diode temperature. 10 ADD0 SMBus Slave Address Select Pin 11 ALERT SMBus Alert (interrupt) Output, Open Drain 12 SMBDATA SMBus Serial-Data Input/Output, Open Drain 14 SMBCLK SMBus Serial-Clock Input Hardware Standby Input. Temperature and comparison threshold data are retained in standby mode. 15 STBY Low = standby mode, high = operate mode. ADC and Multiplexer Detailed Description The ADC is an averaging type that integrates over a The MAX1619 is a temperature sensor designed to work 60ms period (each channel, typical) with excellent in conjunction with an external microcontroller (µC) or noise rejection. other intelligence in thermostatic, process-control, or The multiplexer automatically steers bias currents monitoring applications. The µC is typically a power- through the remote and local diodes, measures their management or keyboard controller, generating SMBus forward voltages, and computes their temperatures. serial commands either by “bit-banging” general-pur- Both channels are automatically converted once the pose input/output (GPIO) pins or through a dedicated conversion process has started, either in free-running SMBus interface block. or single-shot mode. If one of the two channels is not Essentially an 8-bit serial analog-to-digital converter used, the device still performs both measurements, and (ADC) with a sophisticated front end, the MAX1619 the user can simply ignore the results of the unused contains a switched current source, a multiplexer, an channel. ADC, an SMBus interface, and associated control logic The DXN input is biased at 0.65V above ground by an (Figure 1). Temperature data from the ADC is loaded internal diode to set up the analog-to-digital (A/D) into two data registers (local and remote). The remote inputs for a differential measurement. The worst-case temperature data is automatically compared with data DXP–DXN differential input voltage range is 0.25V to previously stored in four temperature-alarm threshold 0.95V. registers. One pair of alarm-threshold registers is used Excess resistance in series with the remote diode caus- to provide hysteretic fan control; the other pair is used es about +1/2°C error per ohm. Likewise, 200µV of off- for alarm interrupt. The local temperature data is avail- set voltage forced on DXP–DXN causes about 1°C error. able for monitoring. 6 _______________________________________________________________________________________ MAX1619 MAX1619 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface Figure 1. Functional Diagram _______________________________________________________________________________________ 7 V CC STBY ADD0 ADD1 ADDRESS DECODER MUX 7 2 DXP + MAX1619 REMOTE DXN + SMBDATA ADC CONTROL SMBus - LOGIC + - SMBCLK LOCAL - READ WRITE GND DIODE 88 FAULT 8 REMOTE TEMPERATURE LOCAL TEMPERATURE COMMAND BYTE DATA REGISTER DATA REGISTER (INDEX) REGISTER 8 HIGH-TEMPERATURE THRESHOLD HIGH-TEMPERATURE THRESHOLD 8 STATUS BYTE REGISTER (REMOTE T ) (REMOTE T ) HIGH MAX LOW-TEMPERATURE THRESHOLD HYSTERESIS THRESHOLD CONFIGURATION (REMOTE T ) (REMOTE T ) BYTE REGISTER LOW HYST 8 8 CONVERSION RATE DIGITAL COMPARATOR DIGITAL COMPARATOR REGISTER (REMOTE OVERTEMP) (REMOTE) ALERT SELECTED VIA ALERT RESPONSE QS SLAVE ADD = 0001 100 ADDRESS REGISTER R OVERT S Q R POL Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface A/D Conversion Sequence Table 1. Remote-Sensor Transistor If a Start command is written (or generated automatical- Manufacturers ly in the free-running auto-convert mode), both channels are converted, and the results of both measurements MANUFACTURER MODEL NUMBER are available after the end of conversion. A BUSY status Central Semiconductor (USA) CMPT3904 bit in the status byte shows that the device is actually performing a new conversion; however, even if the ADC Fairchild Semiconductor (USA) MMBT3904 is busy, the results of the previous conversion are Motorola (USA) MMBT3904 always available. Rohm Semiconductor (Japan) SST3904 Remote-Diode Selection Siemens (Germany) SMBT3904 Temperature accuracy depends on having a good-qual- ity, diode-connected small-signal transistor. Accuracy Zetex (England) FMMT3904CT-ND has been experimentally verified for all the devices list- ed in Table 1. The MAX1619 can also directly measure Note: Transistors must be diode-connected (base shorted to collector). the die temperature of CPUs and other integrated cir- cuits having on-board temperature-sensing diodes. The transistor must be a small-signal type with a rela- worst-case error occurs when auto-converting at the tively high forward voltage; otherwise, the A/D input fastest rate and simultaneously sinking maximum cur- voltage range can be violated. The forward voltage rent at the ALERT and OVERT outputs. For example, at must be greater than 0.25V at 10µA; check to ensure an 8Hz rate and with ALERT and OVERT each sinking this is true at the highest expected temperature. The 1mA, the typical power dissipation is: forward voltage must be less than 0.95V at 100µA; (V )(450µA) + 2(0.4V)(1mA) CC check to ensure this is true at the lowest expected Package qis about 120°C/W, so with V = 5V and JA CC temperature. Large power transistors don’t work. Also, no copper PC board heatsinking, the resulting tempera- ensure that the base resistance is less than 100Ω. Tight ture rise is: specifications for forward-current gain (+50 to +150, for example) indicate that the manufacturer has good ΔT = 3.1mW(120°C/W) = 0.36°C process controls and that the devices have consistent Even with these contrived circumstances, it is difficult V characteristics. BE to introduce significant self-heating errors. For heatsink mounting, the 500-32BT02-000 thermal ADC Noise Filtering sensor from Fenwal Electronics is a good choice. This The ADC is an integrating type with inherently good device consists of a diode-connected transistor, an noise rejection, especially of low-frequency signals such aluminum plate with screw hole, and twisted-pair cable as 60Hz/120Hz power-supply hum. Micropower opera- (Fenwal Inc., Milford, MA, 508-478-6000). tion places constraints on high-frequency noise rejection; Thermal Mass and Self-Heating therefore, careful PC board layout and proper external Thermal mass can seriously degrade the MAX1619’s noise filtering are required for high-accuracy remote effective accuracy. The thermal time constant of the measurements in electrically noisy environments. QSOP-16 package is about 4sec in still air. To settle to High-frequency EMI is best filtered at DXP and DXN within +1°C after a sudden +100°C change, the with an external 2200pF capacitor. This value can be MAX1619 junction temperature requires about five time increased to about 3300pF (max), including cable constants. The use of smaller packages for remote sen- capacitance. Capacitance higher than 3300pF intro- sors, such as SOT23s, improves the situation. Take duces errors due to the rise time of the switched cur- care to account for thermal gradients between the heat rent source. source and the sensor, and ensure that stray air cur- Nearly all noise sources tested cause the ADC measure- rents across the sensor package do not interfere with ments to be higher than the actual temperature, typically measurement accuracy. by +1°C to +10°C, depending on the frequency and Self-heating does not significantly affect measurement amplitude (see Typical Operating Characteristics). accuracy. Remote-sensor self-heating due to the diode current source is negligible. For the local diode, the 8 _______________________________________________________________________________________ MAX1619 MAX1619 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface PC Board Layout 1) Place the MAX1619 as close as practical to the GND remote diode. In a noisy environment, such as a 10 MILS computer motherboard, this distance can be 4 inch- 10 MILS DXP es to 8 inches (typical) or more as long as the worst noise sources (such as CRTs, clock generators, MINIMUM memory buses, and ISA/PCI buses) are avoided. 10 MILS DXN 2) Do not route the DXP–DXN lines next to the deflec- 10 MILS tion coils of a CRT. Also, do not route the traces GND across a fast memory bus, which can easily intro- duce +30°C error, even with good filtering. Otherwise, most noise sources are fairly benign. Figure 2. Recommended DXP/DXN PC Traces 3) Route the DXP and DXN traces in parallel and in • Use guard traces flanking DXP and DXN and con- close proximity to each other, away from any high- necting to GND. voltage traces such as +12V . Leakage currents DC • Place the noise filter and the 0.1µF V bypass CC from PC board contamination must be dealt with capacitors close to the MAX1619. carefully, since a 10MΩ leakage path from DXP to ground causes about +1°C error. • Add a 200Ω resistor in series with V for best noise CC filtering (see Typical Operating Circuit). 4) Connect guard traces to GND on either side of the DXP–DXN traces (Figure 2). With guard traces in Twisted Pair and Shielded Cables place, routing near high-voltage traces is no longer For remote-sensor distances longer than 8 inches, or in an issue. particularly noisy environments, a twisted pair is recom- 5) Route through as few vias and crossunders as possi- mended. Its practical length is 6 feet to 12 feet (typical) ble to minimize copper/solder thermocouple effects. before noise becomes a problem, as tested in a noisy electronics laboratory. For longer distances, the best 6) When introducing a thermocouple, make sure that solution is a shielded twisted pair like that used for audio both the DXP and the DXN paths have matching microphones. For example, the Belden 8451 works well thermocouples. In general, PC board-induced ther- in a noisy environment for distances up to 100 feet. mocouples are not a serious problem. A copper-sol- Connect the twisted pair to DXP and DXN and the shield der thermocouple exhibits 3µV/°C, and it takes to GND, and leave the shield’s remote end unterminated. about 200µV of voltage error at DXP–DXN to cause a +1°C measurement error. So, most parasitic ther- Excess capacitance at DX_ limits practical remote sen- mocouple errors are swamped out. sor distances (see Typical Operating Characteristics). For very long cable runs, the cable’s parasitic capaci- 7) Use wide traces. Narrow ones are more inductive tance often provides noise filtering, so the 2200pF and tend to pick up radiated noise. The 10 mil capacitor can often be removed or reduced in value. widths and spacings recommended in Figure 2 aren’t absolutely necessary (as they offer only a Cable resistance also affects remote-sensor accuracy; minor improvement in leakage and noise), but try to 1Ω series resistance introduces about +1/2°C error. use them where practical. Low-Power Standby Mode 8) Keep in mind that copper can’t be used as an EMI Standby mode disables the ADC and reduces the sup- shield, and only ferrous materials, such as steel, work ply-current drain to 3µA (typical). Enter standby mode well. Placing a copper ground plane between the by forcing the STBY pin low or via the RUN/STOP bit in DXP-DXN traces and traces carrying high-frequency the configuration byte register. Hardware and software noise signals does not help reduce EMI. standby modes behave almost identically: all data is retained in memory, and the SMB interface is alive and PC Board Layout Checklist listening for reads and writes. The only difference is • Place the MAX1619 close to a remote diode. that in hardware standby mode, the one-shot command • Keep traces away from high voltages (+12V bus). does not initiate a conversion. • Keep traces away from fast data buses and CRTs. Standby mode is not a shutdown mode. With activity on • Use recommended trace widths and spacings. the SMBus, extra supply current is drawn (see Typical Operating Characteristics). In software standby mode, • Place a ground plane under the traces. _______________________________________________________________________________________ 9 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface the MAX1619 can be forced to perform A/D conversions Operating Characteristics). Between conversions, the via the one-shot command, despite the RUN/STOP bit instantaneous supply current is about 25µA due to the being high. current consumed by the conversion rate timer. In standby mode, supply current drops to about 3µA. At Activate hardware standby mode by forcing the STBY very low supply voltages (under the power-on-reset pin low. In a notebook computer, this line may be con- threshold), the supply current is higher due to the nected to the system SUSTAT# suspend-state signal. address pin bias currents. It can be as high as 100µA, The STBY pin low state overrides any software conversion depending on ADD0 and ADD1 settings. command. If a hardware or software standby command is received while a conversion is in progress, the conver- SMBus Digital Interface sion cycle is truncated, and the data from that conversion From a software perspective, the MAX1619 appears as a is not latched into either temperature reading register. set of byte-wide registers that contain temperature data, The previous data is not changed and remains available. alarm threshold values, or control bits. A standard SMBus 2-wire serial interface is used to read tempera- The OVERT output continues to function in both hard- ture data and write control bits and alarm threshold data. ware and software standby modes. If the overtemp lim- Each A/D channel within the device responds to the its are adjusted while in standby mode, the digital same SMBus slave address for normal reads and writes. comparator checks the new values and puts the OVERT pin in the correct state based on the last valid ADC con- The MAX1619 employs four standard SMBus protocols: version. The last valid ADC conversion may include a Write Byte, Read Byte, Send Byte, and Receive Byte conversion performed using the one-shot command. (Figure 3). The shorter Receive Byte protocol allows quicker transfers, provided that the correct data register Supply-current drain during the 125ms conversion peri- was previously selected by a Read Byte instruction. Use od is always about 450µA. Slowing down the conversion caution with the shorter protocols in multi-master sys- rate reduces the average supply current (see Typical Write Byte Format S ADDRESS WR ACK COMMAND ACK DATA ACK P 7 bits 8 bits 8 bits 1 Slave Address: Command Byte: selects Data Byte: data goes into the register equivalent to chip-select which register you are set by the command byte (to set line of a 3-wire interface writing to thresholds, configuration masks, and sampling rate) Read Byte Format S ADDRESS WR ACK COMMAND ACK S ADDRESS RD ACK DATA /// P 7 bits 8 bits 7 bits 8 bits Slave Address: Command Byte: selects Slave Address: repeated Data Byte: reads from equivalent to which register you are due to change in data- the register set by the chip-select line reading from flow direction command byte Send Byte Format Receive Byte Format S ADDRESS WR ACK COMMAND ACK P S ADDRESS RD ACK DATA /// P 7 bits 8 bits 7 bits 8 bits Data Byte: reads data from Command Byte: sends com- the register commanded mand with no data; usually by the last Read Byte or used for one-shot command Write Byte transmission; also used for SMBus Alert S = Start condition Shaded = Slave transmission Response return address P = Stop condition /// = Not acknowledged Figure 3. SMBus Protocols 10 ______________________________________________________________________________________ MAX1619 MAX1619 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface tems, since a second master could overwrite the com- Table 2. Data Format (Two’s Complement) mand byte without informing the first master. DIGITAL OUTPUT ROUNDED The temperature data format is 7 bits plus sign in two’s TEMP. DATA BITS TEMP. complement form for each channel, with each data bit rep- (°C) (°C) resenting 1°C (Table 2), transmitted MSB first. Measure- SIGN MSB LSB ments are offset by +1/2°C to minimize internal rounding +130.00 +127 0 111 1111 errors; for example, +99.6°C is reported as +100°C. +127.00 +127 0 111 1111 Alarm Threshold Registers +126.50 +127 0 111 1111 Two registers store ALERT threshold limits, with high- +126.00 +126 0 111 1110 temperature (T ) and low-temperature (T ) reg- HIGH LOW +25.25 +25 0 001 1001 isters for the remote A/D channel. There are no +0.50 +1 0 000 0001 comparison registers for the local A/D channel. If either measured temperature equals or exceeds the corre- +0.25 0 0 000 0000 sponding alarm threshold value, an ALERT interrupt is 0.00 0 0 000 0000 asserted. The power-on-reset (POR) state of the T HIGH -0.25 0 0 000 0000 register is full scale (0111 1111, or +127°C). The POR state of the T register is 1100 1001 or -55°C. -0.50 0 0 000 0000 LOW Two additional alarm threshold registers control the -0.75 -1 1 111 1111 OVERT output (see OVERT Alarm Output section), T MAX -1.00 -1 1 111 1111 and T . The POR state of T is +100°C, and HYST MAX -25.00 -25 1 110 0111 T is +95°C. HYST -25.50 -25 1 110 0111 O OV VE ER RT T Alarm Output for Fan Control -54.75 -55 1 100 1001 The OVERT output is an unlatched open-drain output that -55.00 -55 1 100 1001 behaves as a thermostat to control a fan (Figure 4). When using the SMBus interface, the polarity of the OVERT pin -65.00 -65 1 011 1111 (active-low at POR) can be inverted via bit 5 in the config- -70.00 -65 1 011 1111 uration byte. OVERT’s current state can be read in the status byte. +3V TO +5.5V OVERT can also be used to control a fan without system intervention. OVERT goes low when the remote tempera- +12V ture rises above T and won’t go high again until the MAX STBY V CC temperature drops below T . The power-up default HYST settings for T and T (+100°C and +95°C, MAX HYST MAX1619 respectively) allow the MAX1619 to be used in stand- SMBUS alone thermostat applications where connection to an SMBCLK SERIAL SMBus serial bus isn’t required. SMBDATA INTERFACE (TO HOST) ALERT Diode Fault Alarm DXP There is a continuity fault detector at DXP that detects whether the remote diode has an open-circuit condi- tion. At the beginning of each conversion, the diode DXN fault is checked, and the status byte is updated. This OVERT 2N3904 fault detector is a simple voltage detector; if DXP rises ADD0 above V - 1V (typical) due to the diode current CC source, a fault is detected. Note that the diode fault ADD1 isn’t checked until a conversion is initiated, so immedi- GND PGND ately after power-on reset the status byte indicates no fault is present, even if the diode path is broken. Figure 4. Fan Control Application ______________________________________________________________________________________ 11 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface If the remote channel is shorted (DXP to DXN or DXP to interrupt and reads the Alert Response address, clear- GND), the ADC reads 0000 0000 so as not to trip either ing the interrupt. The system may also read the status the T or T alarms at their POR settings. In byte at this time. The condition that caused the interrupt HIGH LOW applications that are never subjected to 0°C in normal persists, but no new ALERT interrupt is issued. Finally, operation, a 0000 0000 result can be checked to indi- the host writes a new value to T . This enables the HIGH cate a fault condition in which DXP is accidentally short device to generate a new T interrupt if the alert HIGH circuited. Similarly, if DXP is short circuited to V , the condition still exists. CC ADC reads +127°C for both remote and local channels, Alert Response Address and the ALERT and OVERT outputs are activated. The SMBus Alert Response interrupt pointer provides A AL LE ER RT T Interrupts quick fault identification for simple slave devices that lack The ALERT interrupt output signal is latched and can the complex, expensive logic needed to be a bus master. only be cleared by reading the Alert Response address. Upon receiving an ALERT interrupt signal, the host mas- Interrupts are generated in response to T and T ter can broadcast a Receive Byte transmission to the HIGH LOW comparisons and when the remote diode is disconnect- Alert Response slave address (0001 100). Then any slave ed (for continuity fault detection). The interrupt does not device that generated an interrupt attempts to identify halt automatic conversions; new temperature data con- itself by putting its own address on the bus (Table 3). tinues to be available over the SMBus interface after The Alert Response can activate several different slave ALERT is asserted. The interrupt output pin is open-drain 2 devices simultaneously, similar to the I C™ General so that devices can share a common interrupt line. The Call. If more than one slave attempts to respond, bus interrupt rate can never exceed the conversion rate. arbitration rules apply, and the device with the lower The interface responds to the SMBus Alert Response address code wins. The losing device does not gener- address, an interrupt pointer return-address feature ate an acknowledge and continues to hold the ALERT (see Alert Response Address section). Prior to taking line low until serviced (implies that the host interrupt corrective action, always check to ensure that an inter- input is level-sensitive). Successful reading of the alert rupt is valid by reading the current temperature. response address clears the interrupt latch. To prevent reoccurring interrupts, the MAX1619 asserts Command Byte Functions ALERT only once per crossing of a given temperature The 8-bit command byte register (Table 4) is the master threshold. To enable a new interrupt, the value in the index that points to the other registers within the limit register that triggered the interrupt must be rewrit- MAX1619. The register’s POR state is 0000 0001 so ten. Note that other interrupt conditions can be caused that a Receive Byte transmission (a protocol that lacks by crossing the opposite temperature threshold, or a the command byte) that occurs immediately after POR diode fault can still cause an interrupt. returns the current remote temperature data. Example: the remote temperature reading crosses The one-shot command immediately forces a new conver- T , activating ALERT. The host responds to the HIGH sion cycle to begin. In software standby mode (RUN/STOP bit = high), a new conversion is begun, after Table 3. Read Format for Alert Response which the device returns to standby mode. If a conversion Address (0001100) is in progress when a one-shot command is received, the command is ignored. If a one-shot command is received BIT NAME FUNCTION in auto-convert mode (RUN/STOP bit = low) between con- 7 ADD7 versions, a new conversion begins, the conversion rate (MSB) timer is reset, and the next automatic conversion takes 6 ADD6 place after a full delay elapses. 5 ADD5 Provide the current MAX1619 slave address 4 ADD4 Configuration Byte Functions The configuration byte register (Table 5) is used to 3 ADD3 mask (disable) interrupts, to put the device in software 2 ADD2 standby mode, to change the polarity of the OVERT 1 ADD1 output, and to enable the write-once protection. The 0 1 Logic 1 lowest two bits are internally set to zeros, making them (LSB) “don’t care” bits. This register’s contents can be read back over the serial interface. 2 I C is a trademark of Philips Corp. 12 ______________________________________________________________________________________ MAX1619 MAX1619 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface Table 4. Command-Byte Bit Assignments REGISTER COMMAND POR STATE FUNCTION RLTS 00h 0000 0000* Read local temperature: returns latest temperature RRTE 01h 0000 0000* Read remote temperature: returns latest temperature RSL 02h N/A Read status byte (flags, busy signal) RCL 03h 0000 1100 Read configuration byte RCRA 04h 0000 0010 Read conversion rate byte RRTM 10h 01100100 Read remote T limit MAX RRTH 11h 01011111 Read remote T limit HYST RRHI 07h 0111 1111 Read remote T limit HIGH RRLS 08h 1100 1001 Read remote T limit LOW WCA 09h N/A Write configuration byte WCRW 0Ah N/A Write conversion rate byte WRTM 12h N/A Write remote T limit MAX WRTH 13h N/A Write remote T limit HYST WRHA 0Dh N/A Write remote T limit HIGH WRLN 0Eh N/A Write remote T limit LOW OSHT 0Fh N/A One-shot command SPOR FCh N/A Write software POR WADD FDh N/A Write address MFG ID FEh 0100 1101 Read manufacturer ID code DEV ID FFh 0000 0100 Read device ID code *If the device is in hardware standby mode at POR, both temperature registers read 0°C. Table 5. Configuration-Byte Bit Assignments BIT NAME POR STATE FUNCTION 7 (MSB) MASK 0 Masks all ALERT interrupts when high. Standby mode control bit. If high, the device immediately stops converting and RUN/ 6 0 enters standby mode. If low, the device converts in either one-shot or timer STOP mode. Determines the polarity of the OVERT output: 5 POL 0 0 = active low (low when overtemp) 1 = active high When asserted high, locks out all subsequent writes to: [] Configuration register bits 6, 5, 4, 3, 2 (RUN/STOP, POL, PROT, ID1, ID2) [] T register MAX 4 PROT 0 [] T register HYST [] Conversion rate register [] Diode Current 3 ID1 1 Reduces the diode current by 5µA when set low. 2 ID2 1 Reduces the diode current by 2.5µA when set low. 1–0 RFU 0 Reserved for future use. ______________________________________________________________________________________ 13 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface Table 6. Status-Byte Bit Assignments Table 7. Conversion-Frequency Control Byte BIT NAME FUNCTION CONVERSION AVERAGE SUPPLY 7 A high indicates that the ADC is busy BUSY DATA FREQUENCY CURRENT (MSB) converting. (Hz) (µA typ, at V = 3.3V) CC 6 RFU Reserved for future use. 00h 0.0625 30 5 RFU Reserved for future use. 01h 0.125 33 A high indicates that the remote high- 4 RHIGH* temperature alarm has activated. 02h 0.25 35 A high indicates that the remote low- 03h 0.5 48 3 RLOW* temperature alarm has activated. 04h 1 70 A high indicates a remote-diode conti- 2 OPEN* 05h 2 128 nuity (open-circuit) fault. 06h 4 225 This bit follows the state of the OVERT 1 OVER 07h 8 425 pin exactly, in real time (unlatched). 08h to 0 RFU — RFU Reserved for future use. FFh (LSB) *The HIGH and LOW temperature alarm flags stay high until Conversion Rate Byte cleared by POR or until status register is read. The conversion rate register (Table 7) programs the time interval between conversions in free-running autoconvert Write-Once Protection mode. This variable rate control reduces the supply cur- Write-once protection allows the host BIOS code to rent in portable-equipment applications. The conversion configure the MAX1619 in a particular way, and then rate byte’s POR state is 02h (0.25Hz). The MAX1619 protect that configuration against data corruption in the looks only at the 3 LSB bits of this register, so the upper 5 host that might cause spurious writes to the MAX1619. bits are “don’t care” bits, which should be set to zero. The In particular, write protection allows a foolproof over- conversion rate tolerance is ±25% at any rate setting. temperature override that forces the fan on 100% via Valid A/D conversion results for both channels are avail- OVERT independent of the host system. The write-pro- able one total conversion period (125ms nominal, 156ms tection bit (bit 4), once set high, can’t be reset to low maximum) after initiating a conversion, whether conver- except by a hardware power-on reset. A SPOR (soft- sion is initiated via the RUN/STOP bit, hardware STBY ware POR) will not reset this bit. pin, one-shot command, or initial power-up. Changing the conversion rate can also affect the delay until new results Status Byte Functions are available (Table 8). The status byte register (Table 6) indicates which (if any) temperature thresholds have been exceeded. This Manufacturer and Device ID Codes byte also indicates whether or not the ADC is converting Two ROM registers provide manufacturer and device ID and whether there is an open circuit in the remote diode codes (Table 4). Reading the manufacturer ID returns DXP–DXN path. The status byte is cleared by any suc- 4Dh, which is the ASCII code “M” (for Maxim). Reading cessful read of the status byte, unless the fault persists. the device ID returns 04h, indicating a MAX1619 device. The status of bit1 (OVER) follows the state of OVERT If READ WORD 16-bit SMBus protocol is employed exactly. Note that the ALERT interrupt latch is not auto- (rather than the 8-bit READ BYTE), the least significant matically cleared when the status flag bit is cleared. byte contains the data and the most significant byte con- When autoconverting, if the T and T limits are HIGH LOW tains 00h in both cases. close together, it’s possible for both high-temp and low- temp status bits to be set, depending on the amount of Slave Addresses time between status read operations (especially when The MAX1619 appears to the SMBus as one device converting at the fastest rate). In these circumstances, it’s having a common address for both ADC channels. The best not to rely on the status bits to indicate reversals in device address can initially be set to one of nine differ- long-term temperature changes. Instead, use a current ent values by pin-strapping ADD0 and ADD1 so that temperature reading to establish the trend direction. more than one MAX1619 can reside on the same bus without address conflicts (Table 9). 14 ______________________________________________________________________________________ MAX1619 MAX1619 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface Table 8. RLTS and RRTE Temperature Register Update Timing Chart NEW CONVERSION TIME UNTIL RLTS AND RRTE OPERATING MODE CONVERSION INITIATED BY: FREQUENCY (CHANGED VIA ARE UPDATED WRITE TO WCRW) Autoconvert Power-on reset n/a (0.25Hz) 156ms max One-shot command, while idling Autoconvert n/a 156ms max between automatic conversions One-shot command that occurs When current conversion is Autoconvert n/a during a conversion complete (1-shot is ignored) Autoconvert Rate timer 0.0625Hz 20sec Autoconvert Rate timer 0.125Hz 10sec Autoconvert Rate timer 0.25Hz 5sec Autoconvert Rate timer 0.5Hz 2.5sec Autoconvert Rate timer 1Hz 1.25sec Autoconvert Rate timer 2Hz 625ms Autoconvert Rate timer 4Hz 312.5ms Autoconvert Rate timer 8Hz 237.5ms Hardware Standby n/a 156ms STBY pin Software Standby RUN/STOP bit n/a 156ms Software Standby One-shot command n/a 156ms below 1.7V (typical, see Electrical Characteristics table). Table 9. POR Slave Address Decoding When power is first applied and V rises above 1.75V CC (ADD0 and ADD1) (typical), the logic blocks begin operating, although reads ADD0 ADD1 ADDRESS and writes at V levels below 3V are not recommended. CC A second V comparator, the ADC UVLO comparator, GND GND 0011 000 CC prevents the ADC from converting until there is sufficient GND High-Z 0011 001 headroom (V = 2.8V typical). CC GND V 0011 010 CC The SPOR software POR command can force a power-on High-Z GND 0101 001 reset of the MAX1619 registers via the serial interface. Use High-Z High-Z 0101 010 the SEND BYTE protocol with COMMAND = FCh. This is High-Z V 0101 011 CC most commonly used to reconfigure the slave address of V GND 1001 100 CC the MAX1619 “on the fly,” where external hardware has V High-Z 1001 101 CC forced new states at the ADD0 and ADD1 address pins V V 1001 110 CC CC prior to the software POR. The new address takes effect Note: High-Z means that the pin is left unconnected and floating. less than 100µs after the SPOR transmission stop condition. Power-Up Defaults: The address pin states are checked at POR and SPOR • Interrupt latch is cleared. only, and the address data stays latched to reduce qui- escent supply current due to the bias current needed • Address select pins are sampled. for high-Z state detection. A new device address can be • ADC begins auto-converting at a 0.25Hz rate. written using the Write Address Command FDh. • Command byte is set to 01h to facilitate quick The MAX1619 also responds to the SMBus Alert Response remote Receive Byte queries. slave address (see the Alert Response Address section). • T and T registers are set to +127°C and HIGH LOW POR and UVLO -55°C, respectively. The MAX1619 has a volatile memory. To prevent ambig- • T and T are set to +100°C and +95°C, MAX HYST uous power-supply conditions from corrupting the data in respectively. memory and causing erratic behavior, a POR voltage • OVERT polarity is active low. detector monitors V and clears the memory if V falls CC CC ______________________________________________________________________________________ 15 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface AB C D EFG H I J K t tHIGH LOW SMBCLK SMBDATA t t t t t SU:STA HD:STA SU:DAT SU:STO BUF A = START CONDITION E = SLAVE PULLS SMBDATA LINE LOW I = ACKNOWLEDGE CLOCK PULSE B = MSB OF ADDRESS CLOCKED INTO SLAVE F = ACKNOWLEDGE BIT CLOCKED INTO MASTER J = STOP CONDITION C = LSB OF ADDRESS CLOCKED INTO SLAVE G = MSB OF DATA CLOCKED INTO MASTER K = NEW START CONDITION D = R/W BIT CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO MASTER Figure 5. SMBus Write Timing Diagram AB C D EFG H I J K L M t t LOW HIGH SMBCLK SMBDATA t t t t SU:STA HD:STA SU:DAT HD:DAT t t SU:STO BUF A = START CONDITION F = ACKNOWLEDGE BIT CLOCKED INTO MASTER J = ACKNOWLEDGE CLOCKED INTO MASTER B = MSB OF ADDRESS CLOCKED INTO SLAVE G = MSB OF DATA CLOCKED INTO SLAVE K = ACKNOWLEDGE CLOCK PULSE C = LSB OF ADDRESS CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO SLAVE L = STOP CONDITION, DATA EXECUTED BY SLAVE D = R/W BIT CLOCKED INTO SLAVE I = SLAVE PULLS SMBDATA LINE LOW M = NEW START CONDITION E = SLAVE PULLS SMBDATA LINE LOW Figure 6. SMBus Read Timing Diagram 16 ______________________________________________________________________________________ MAX1619 MAX1619 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface Listing 1. Pseudocode Example ______________________________________________________________________________________ 17 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface Listing 1. Pseudocode Example (continued) 18 ______________________________________________________________________________________ MAX1619 MAX1619 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface Listing 1. Pseudocode Example (continued) Programming Example: Note: Thermal management decisions should be made based on the latest external temperature obtained from Clock-Throttling Control for CPUs the MAX1619 rather than the value of the Status Byte. Listing 1 gives an untested example of pseudocode for The MAX1619 responds very quickly to changes in its proportional temperature control of Intel mobile CPUs environment due to its sensitivity. High and low alarm through a power-management microcontroller. This conditions can exist at the same time in the Status Byte program consists of two main parts: an initialization rou- due to the MAX1619 correctly reporting environmental tine and an interrupt handler. The initialization routine changes around it. checks for SMBus communications problems and sets up the MAX1619 configuration and conversion rate. The interrupt handler responds to ALERT signals by reading Chip Information the current temperature and setting a CPU clock duty factor proportional to that temperature. The relationship TRANSISTOR COUNT: 11,487 between clock duty and temperature is fixed in a look- up table contained in the microcontroller code. ______________________________________________________________________________________ 19 Remote/Local Temperature Sensor with Dual- Alarm Outputs and SMBus Serial Interface Package Information Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 20 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 © 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX1619 QSOP.EPS