ADM1032

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REV.0 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 rights of third parties that may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. a ADM1032* Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 2001 /H115501/H11543C Remote and Local System Temperature Monitor FUNCTIONAL BLOCK DIAGRAM ON-CHIP TEMPERATURE SENSOR A-TO-D CONVERTER BUSY RUN/STANDBY EXTERNAL DIODE OPEN-CIRCUIT ADDRESS POINTER REGISTER CONVERSION RATE REGISTER REMOTE TEMPERATURE HIGH-LIMIT REGISTER CONFIGURATION REGISTER INTERRUPT MASKING LIMIT COMPARATOR REMOTE TEMPERATURE VALUE REGISTER LOCAL TEMPERATURE VALUE REGISTER VDD GND SDATA SCLK THERM ALERT D– REMOTE TEMPERATURE LOW-LIMIT REGISTER LOCAL TEMPERATURE HIGH-LIMIT REGISTER LOCAL TEMPERATURE LOW-LIMIT REGISTER ANALOG MUX ADM1032 LOCAL THERM LIMIT REGISTER EXTERNAL THERM LIMIT REGISTER DIGITAL MUX DIGITAL MUX STATUS REGISTER SMBUS INTERFACE REMOTE OFFSET REGISTER

FEATURES

On-Chip and Remote Temperature Sensing Offset Registers for System Calibration 0.125/H11543C Resolution/1 /H11543C Accuracy on Remote Channel 1/H11543C Resolution/3 /H11543C Accuracy on Local Channel Fast (Up to 64 Measurements per Second) 2-Wire SMBus Serial Interface Supports SMBus Alert Programmable Over/Under Temperature Limits Programmable Fault Queue Over-Temperature Fail-Safe THERM Output Programmable THERM Limits Programmable THERM Hysteresis 170 /H9262A Operating Current 5.5 /H9262A Standby Current 3 V to 5.5 V Supply Small 8-Lead SO and Micro_SO Package

APPLICATIONS

Pentium is a registered trademark of Intel Corporation. PRODUCT DESCRIPTION The ADM1032 is a dual-channel digital thermometer and under/over temperature alarm, intended for use in p ersonal computers and thermal management systems. The higher 1 °C accuracy offered allows systems designers to safely reduce temperature guardbanding and increase system performance. The device can measure the temperature of a microprocessor using a diode-connected NPN or PNP transistor, which may be provided on-chip or can be a low-cost discrete device such as the 2N3906. A novel measurement technique cancels out the absolute value of the transistor’s base emitter voltage, so that no calibration is required. The second measurement channel mea- sures the output of an on-chip temp erature sensor, to monitor the temperature of the device and its en vironment. The ADM1032 communicates over a two-wire serial interface compatible with System Management Bus (SMBus) standards. Under and over temperature limits can be programmed into the device over the serial bus, and an ALERT output signals when the on-chip or remote temperature measurement is out of range. This output can be used as an interrupt, or as an SMBus alert. The THERM output is a comparator output that allows CPU clock throttling or on/off control of a cooling fan.

REV. 0–2– ADM1032–SPECIFICATIONS(TA = TMIN to TMAX, VDD = VMIN to VMAX, unless otherwise noted.) Parameter Min Typ Max Unit Test Conditions/Comments POWER SUPPLY Supply Voltage, VDD 3.0 3.30 5.5 V Average Operating Supply Current, I CC 170 215 µA 0.0625 Conversions/Sec Rate 1 5.5 10 µA Standby Mode Undervoltage Lockout Threshold 2.35 2.55 2.8 V V DD Input, Disables ADC, Rising Edge Power-On Reset Threshold 1 2.4 V TEMPERATURE-TO-DIGITAL CONVERTER Local Sensor Accuracy ±1 ±3 °C0 ≤ TA ≤ 100°C, VCC = 3 V to 3.6 V Resolution 1 °C Remote Diode Sensor Accuracy ±1 °C6 0 °C ≤ TD ≤ 100°C, VCC = 3 V to 3.6 V Resolution 0.125 °C Remote Sensor Source Current 230 µA High Level, Note 2 13 µA Low Level, Note 2 Conversion Time 35.7 142.8 ms From Stop Bit to Conversion Complete (Both Channels) One-Shot Mode with Averaging Switched On 5.7 22.8 ms One-Shot Mode with Averaging Off (i.e., Conversion Rate = 32 or 64 Conversions per Second) OPEN-DRAIN DIGITAL OUTPUTS (THERM, ALERT) Output Low Voltage, V OL 0.4 V I OUT = –6.0 mA2 High Level Output Leakage Current, I OH 0.1 1 µAV OUT = VDD SMBus INTERFACE2 Logic Input High Voltage, V IH 2.1 V V DD = 3 V to 5.5 V SCLK, SDATA Logic Input Low Voltage, V IL 0.8 V V DD = 3 V to 5.5 V Hysteresis 500 mV SCLK, SDATA SMBus Output Low Sink Current 6 mA SDATA Forced to 0.6 V ALERT Output Low Sink Current 1 mA ALERT Forced to 0.4 V Logic Input Current, I IH, IIL –1 +1 µA SMBus Input Capacitance, SCLK, SDATA 5 pF SMBus Clock Frequency 100 kHz SMBus Timeout 25 64 ms Note 3 SMBus Clock Low Time, t LOW 4.7 µst LOW between 10% Points SMBus Clock High Time, t HIGH 4 µst HIGH between 90% Points SMBus Start Condition Setup Time, t SU:STA 4.7 µs SMBus Start Condition Hold Time, t HD:STA 4 µs Time from 10% of SDATA to 90% of SCLK SMBus Stop Condition Setup Time, t SU:STO 4 µs Time from 90% of SCLK to 10% of SDATA SMBus Data Valid to SCLK Rising Edge 250 ns Time for 10% or 90% of SDATA to Time, tSU:DAT 10% of SCLK SMBus Data Hold Time, t HD:DAT 300 µs SMBus Bus Free Time, t BUF 4.7 µs Between Start/Stop Condition SCLK Falling Edge to SDATA 1 µs Master Clocking in Data Valid Time, tVD,DAT SCLK, SDATA Rise Time, t R 1 µs SCLK, SDATA Fall Time, t F 300 ns NOTES 1See Table VI for information on other conversion rates. 2Guaranteed by Design, not production tested. 3The SMBus timeout is a programmable feature. By default it is not enabled. Details on how to enable it are available in the SMB us section of this data sheet. Specifications subject to change without notice.

Figure 1. Diagram for Serial Bus Timing 1V DD Positive Supply, 3 V to 5.5 V. 2 D+ Positive Connection to Remote Temperature Sensor. 3 D– Negative Connection to Remote Temperature Sensor. temperature condition. Requires pull-up to V DD.

5 GND Supply Ground Connection

6 ALERT Open-Drain Logic Output Used as Interrupt or SMBus Alert. 7 SDATA Logic Input/Output, SMBus Serial Data. Open-Drain Output. Requires pull-up resistor. 8 SCLK Logic Input, SMBus Serial Clock. Requires pull-up resistor. maximum rating conditions for extended periods may affect device reliability.

REV. 0 ADM1032–Typical Performance Characteristics –4– LEAKAGE RESIST ANCE – M/H9024 TEMPERA TURE ERROR – /H11543C 0 10 100 –16 –12 D+ TO GND D+ TO VDD TPC 1. Temperature Error vs. Leakage Resistance FREQUENCY – Hz VIN = 100mV p-p TEMPERA TURE ERROR – /H11543C 10 1M VIN = 250mV p-p TPC 4. Temperature Error vs. Power Supply Noise Frequency VIN = 50mV p-p FREQUENCY – Hz TEMPERA TURE ERROR – /H11543C 100k 1M 10M 100M VIN = 100mV p-p VIN = 25mV p-p TPC 7. Temperature Error vs. Common-Mode Noise Frequency TEMPERA TURE ERROR – /H11543C –0.5 0.5 1.0 TEMPERA TURE – /H11543C 0 2 04 06 08 0 1 0 0 1 2 0 TPC 2. Temperature Error vs. Actual Temperature Using 2N3906 1 6 11 16 21 26 31 TEMPERA TURE ERROR – C CAP ACIT ANCE – nF TPC 5. Temperature Error vs. Capacitance between D+ and D– SCLK FREQUENCY – kHz 1 5 10 25 50 75 100 SUPPL Y CURRENT – /H9262A 250 500 750 1000 VDD = 3.3V VDD = 5V TPC 8. Standby Supply Current vs. Clock Frequency FREQUENCY – Hz 100k 100M 1M TEMPERA TURE ERROR – C 10M VIN = 10mV p-p VIN = 40mV p-p TPC 3. Temperature Error vs. Differential Mode Noise Frequency CONVERSION RA TE – Hz 0.01 2.0 SUPPL Y CURRENT – /H9262A1.5 0.5 VDD = 5V 0.1 1 10 100 1.0 VDD = 3V TPC 6. Operating Supply Current vs. Conversion Rate SUPPL Y VOL T AGE – V ST ANDBY SUPPL Y CURRENT – /H9262A TPC 9. Standby Supply Current vs. Supply Voltage

REV. 0 ADM1032 –6– Status Register Bit 7 of the Status Register indicates that the ADC is busy con- verting when it is high. Bits 6 to 3, 1, and 0 are flags that indicate the results of the limit comparisons. Bit 2 is set when the remote sensor is open circuit. If the local and/or remote temperature measurement is above the corresponding high temperature limit, or below or equal to, the corresponding low temperature limit, one or more of these flags will be set. These five flags (Bits 6 to 2) NOR’d together, so that if any of them is high, the ALERT interrupt latch will be set and the ALERT output will go low. Reading the Status Register will clear the five flag bits, provided the error conditions that caused the flags to be set have gone away. While a limit comparator is tripped due to a value register containing an out-of-limit measure- ment, or the sensor is open circuit, the corresponding flag bit cannot be reset. A flag bit can only be reset if the c orresponding value register contains an in-limit measurement or the sensor is good. The ALERT interrupt latch is not reset by reading the Status Register, but will be reset when the ALERT output has been serviced by the master reading the device address, provided the error condition has gone away and the Status Register flag bits have been reset. When Flags 1 and 0 are set, the THERM output goes low to indicate that the temperature measurements are outside the programmed limits. THERM output does not need to be reset, unlike the ALERT output. Once the measurements are within the limits, the corresponding Status register bits are reset and the THERM output goes high. Table IV. Status Register Bit Assignments Bit Name Function

7 BUSY 1 When ADC Converting

6 LHIGH * 1 When Local High-Temp Limit Tripped

5 LLOW * 1 When Local Low-Temp Limit Tripped

4 RHIGH * 1 When Remote High-Temp Limit Tripped

3 RLOW * 1 When Remote Low-Temp Limit Tripped

2 OPEN * 1 When Remote Sensor Open-Circuit

1 RTHRM 1 When Remote Therm Limit Tripped

0 LTHRM 1 When Local Therm Limit Tripped

*These flags stay high until the status register is read or they are reset by POR. Configuration Register Two bits of the Configuration Register are used. If Bit 6 is 0, which is the power-on default, the device is in operating mode with the ADC converting. If Bit 6 is set to 1, the device is in standby mode and the ADC does not convert. The SMBus does, however, remain active in Standby Mode so values can be read from or written to the SMBus. The ALERT and THERM O/Ps are also active in Standby Mode. Bit 7 of the configuration register is used to mask the alert output. If Bit 7 is 0, which is the power-on default, the output is enabled. If Bit 7 is set to 1, the output is disabled. Table II. Extended Temperature Resolution (Remote Temperature Low Byte) Extended Remote Temperature Resolution Low Byte 0.000°C 0 000 0000 0.125°C 0 010 0000 0.250°C 0 100 0000 0.375°C 0 110 0000 0.500°C 1 000 0000 0.625°C 1 010 0000 0.750°C 1 100 0000 0.875°C 1 110 0000 ADM1032 REGISTERS The ADM1032 contains registers that are used to store the results of remote and local temperature measurements, high and low temperature limits, and to configure and control the device. A description of these registers follows, and further details are given in Tables III to VII. Address Pointer Register The Address Pointer Register itself does not have, or require, an address, as it is the register to which the first data byte of every Write operation is written automatically. This data byte is an address pointer that sets up one of the other registers for the second byte of the Write operation, or for a subsequent read operation. The power-on default value of the Address Po inter Register is 00h, so if a read operation is performed immediately after power- on without first writing to the Address Pointer, the value of the local temperature will be returned, since its register address is 00h. Value Registers The ADM1032 has three registers to store the results of Local and Remote temperature measurements. These registers are written to by the ADC only and can be read over the SMBus. Offset Register Series resistance on the D+ and D– lines in processor packages and clock noise can introduce offset errors into the remote tem- perature measurement. To achieve the specified accuracy on this channel these offsets must be removed. The offset value is stored as an 11-bit, two’s complement value in registers 11h (high byte) and 12h (low byte, left justified). The value of the offset is negative if the MSB of register 11h is 1 and it is positive if the MSB of register 12h is 0. The value is added to the measured value of remote temperature. The offset register powers up with a default value of 0 °C, and will have no effect if nothing is written to them. Table III. Sample Offset Register Codes Offset Value 11h 12h –4°C 1 111 1100 0 000 0000 –1°C 1 111 1111 0 000 0000 –0.125°C 1 111 1111 1 110 0000 0°C 0 000 0000 0 000 0000 +0.125°C 0 000 0000 0 010 0000 +1°C 0 000 0001 0 000 0000 +4°C 0 000 0100 0 000 0000

REV. 0 ADM1032 –7– Consecutive ALERT Register This value written to this register determines how many out-of- limit measurements must occur before an ALERT is generated. The default value is that one out-of-limit measurement gener- ates an ALERT. The max value that can be chosen is 4. The purpose of this register is to allow the user to perform some filter- ing of the output. This is particularly useful at the faster two conversion rates where no averaging takes place. Table VII. Number of “Out-of-Limit” Register Value Measurements Required yxxx 000x 1 yxxx 001x 2 yxxx 011x 3 yxxx 111x 4 NOTES x = Don’t care bit. y = SMBus timeout bit. Default = 0. See SMBus section for more information. SERIAL BUS INTERFACE Control of the ADM1032 is carried out via the serial bus. The ADM1032 is connected to this bus as a slave device, under the control of a master device. There is a programmable SMBus timeout. When this is enabled the SMBus will timeout after typically 25 ms of no activity. How- ever, this feature is not enabled by default. To enable it, set Bit 7 of the Consecutive Alert Register (Addr = 22h). The ADM1032 supports Packet Error Checking (PEC) and its use is optional. It is triggered by supplying the extra clock for the PEC byte. The PEC byte is calculated using CRC-8. The Frame Check Sequence (FCS) conforms to CRC-8 by the polynomial: C(x) = x 8 + x2 + x1 + 1 Consult SMBus 1.1 specification for more information (www.smbus.org). ADDRESSING THE DEVICE In general, every SMBus device has a 7-bit device address (except for some devices that have extended, 10-bit addresses). When the master device sends a device address over the bus, the slave device with that address will respond. The ADM1032 is avail- able with one device address, which is Hex 4C (1001 100). The serial bus protocol operates as follows: 1. The master initiates data transfer by establishing a START condition, defined as a high-to-low transition on the serial data line SDATA, while the serial clock line SCLK remains high. This indicates that an address/data stream will follow. All slave peripherals connected to the serial bus respond to the START condition, and shift in the next eight bits, con- sisting of a 7-bit address (MSB first) plus an R/ W bit, which determines the direction of the data transfer, i.e., whether data will be written to or read from the slave device. The peripheral whose address corresponds to the transmitted address responds by pulling the data line low during the low period before the ninth clock pulse, known as the Acknowl- edge Bit. All other devices on the bus now remain idle while the selected device waits for data to be read from or written Table V. Configuration Register Bit Assignments Power-On Bit Name Function Default

7 MASK1 0 = ALERT Enabled 0

1 = ALERT Masked

6 RUN/STOP 0 = Run 0

1 = Standby 5–0 Reserved 0 Conversion Rate Register The lowest four bits of this register are used to program the conversion rate by dividing the internal oscillator clock by 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, or 1024 to give conversion times from 15.5 ms (code 0Ah) to 16 seconds (code 00h). This register can be written to and read back over the SMBus. The higher four bits of this register are unused and must be set to zero. Use of slower conversion times greatly reduces the device power consumption, as shown in Table VI. Table VI. Conversion Rate Register Codes Average Supply Current Data Conversion/sec mA Typ at V DD = 5.5 V 00h 0.0625 0.17 01h 0.125 0.20 02h 0.25 0.21 03h 0.5 0.24 04h 1 0.29 05h 2 0.40 06h 4 0.61 07h 8 1.1 08h 16 1.9 09h 32 0.73 0Ah 64 1.23 0B to FFh Reserved Limit Registers The ADM1032 has nine Limit Registers to store local and remote, high, low, and THERM temperature limits. These registers can be written to and read back over the SMBus. The high limit registers perform a > comparison while the low limit registers perform a < comparison. For example, if the high limit register is programmed with 80 °C, then measuring 81 oC will result in an alarm condition. If the Low Limit Register is programmed with 0°C, measuring 0°C or lower will result in Alarm condition. Exceeding either the Local or Remote THERM limit asserts THERM low. A default hysteresis value of 10 °C is provided, which applies to both channels. This hysteresis may be reprogrammed to any value after power up (Reg 0x21h). One-Shot Register The One-Shot Register is used to initiate a single conv ersion and comparison cycle when the ADM1032 is in standby mode, after which the device returns to standby. This is not a data register as such, and it is the write operation that causes the one-shot conversion. The data written to this address is irrel- evant and is not stored. The conversion time on a single shot is 96 ms when the conversion rate is 16 conversions per second or less. At 32 conversions per second the conversion time is 15.3 ms. This is because averaging is disabled at the faster conversion rates (32 and 64 conversions per second).

REV. 0 ADM1032 –8– to it. If the R/W bit is a 0, the master will write to the slave device. If the R/W bit is a 1, the master will read from the slave device. 2. Data is sent over the serial bus in sequences of nine clock pulses, eight bits of data followed by an Acknowledge Bit from the slave device. Transitions on the data line must occur during the low period of the clock signal and remain stable during the high period, as a low-to-high transition when the clock is high may be interpreted as a STOP signal. The number of data bytes that can be transmitted over the serial bus in a single Read or Write operation is limited only by what the master and slave devices can handle. 3. When all data bytes have been read or written, stop condi- tions are established. In Write mode, the master will pull the data line high during the tenth clock pulse to assert a STOP condition. In Read mode, the master device will override the acknowledge bit by pulling the data line high during the low period before the ninth clock pulse. This is known as No Acknowledge. The master will then take the data line low during the low period before the tenth clock pulse, then high during the tenth clock pulse to assert a STOP condition. Any number of bytes of data may be transferred over the serial bus in one operation, but it is not possible to mix read and write in one operation because the type of operation is determined at the beginning and cannot subsequently be changed without starting a new operation. In the case of the ADM1032, write operations contain either one or two bytes, while read operations contain one byte, and per- form the following functions: To write data to one of the device data registers or read data from it, the Address Pointer Register must be set so that the correct data register is addressed, then data can be written into that register or read from it. The first byte of a write operation always contains a valid address that is stored in the Address Pointer Register. If data is to be written to the device, the write operation contains a second data byte that is written to the register selected by the address pointer register. This is illustrated in Figure 3a. The device address is sent over the bus followed by R/ W set to 0. This is followed by two data bytes. The first data byte is the address of the internal data register to be written to, which is stored in the Address Pointer Register. The second data byte is the data to be written to the internal data register. When reading data from a register there are two possibilities: 1. If the ADM1032’s Address Pointer Register value is unknown or not the desired value, it is first necessary to set it to the correct value before data can be read from the desired data register. This is done by performing a write to the ADM1032 as before, but only the data byte containing the register read address is sent, as data is not to be written to the register. This is shown in Figure 3b. A read operation is then performed consisting of the serial bus address, R/W bit set to 1, followed by the data byte read from the data register. This is shown in Figure 3c. 2. If the Address Pointer Register is known to be already at the desired address, data can be read from the corresponding data register without first writing to the Address Pointer Register and Figure 3b can be omitted. Table VIII. List of ADM1032 Registers Read Address (Hex) Write Address (Hex) Name Power-On Default Not Applicable Not Applicable Address Pointer Undefined

00 Not Applicable Local Temperature Value 0000 0000 (00h)

01 Not Applicable External Temperature Value High Byte 0000 0000 (00h)

02 Not Applicable Status Undefined

03 09 Configuration 0000 0000 (00h) 04 0A Conversion Rate 0000 1000 (08h) 05 0B Local Temperature High Limit 0101 0101 (55h) (85 °C) 06 0C Local Temperature Low Limit 0000 0000 (00h) (0 °C) 07 0D External Temperature High Limit High Byte 0101 0101 (55h) (85 °C) 08 0E External Temperature Low Limit High Byte 0000 0000 (00h) (0 °C) Not Applicable 0F One-Shot

10 Not Applicable External Temperature Value Low Byte 0000 0000

11 11 External Temperature Offset High Byte 0000 0000 12 12 External Temperature Offset Low Byte 0000 0000 13 13 External Temperature High Limit Low Byte 0000 0000 14 14 External Temperature Low Limit Low Byte 0000 0000 19 19 External THERM Limit 0101 0101 (55h) (85 °C) 20 20 Local THERM Limit 0101 0101 (55h) (85 °C) 21 21 THERM Hysteresis 0000 1010 (0Ah) (10 °C) 22 22 Consecutive ALERT 0000 0001 (01h) FE Not Applicable Manufacturer ID 0100 0001 (41h) FF Not Applicable Die Revision Code Undefined Writing to address 0F causes the ADM1032 to perform a single measurement. It is not a data register as such and it does not mat ter what data is written to it.

1. Master initiates a read operation and sends the Alert Response

must not be used as a specific device address.

1. The device whose ALERT output is low responds to the Alert

Response Address and the master reads its device address. As the device address is seven bits, an LSB of ‘1’ is added.

1. If more than one device’s ALERT output is low, the one with

with normal SMBus arbitration.

1. Once the ADM1032 has responded to the Alert Response

to the corresponding value register. if there are clock and data signals on the bus. generated even though the ADM1032 is still in standby. The ADM1032 has two interrupt outputs, ALERT and THERM. is intended as a “fail-safe” interrupt output that cannot be masked. high temperature limits, no interrupt will be generated. or greater than the high temperature limit programmed.

1. If either temperature measured exceeds the high temperature

limit, the ALERT output will assert low.

1. If the local or remote temperature continues to increase and

should it be at a critical temperature. ent power rail, usually that of the SMBus controller. Figure 5. Operation of the THERM Output measurement as a fault condition.

NPN transistor connected as a diode (base shorted to collector). collector and base are connected to D– and the emitter to D+. cally added to or subtracted from the temperature measurement.

1. Some CPU manufacturers specify the high and low current

must be programmed to the Offset Register.

• Base-emitter voltage greater than 0.25 V at 6 mA, at the highest operating temperature.
• Base-emitter voltage less than 0.95 V at 100 mA, at the lowest operating temperature.
• Base resistance less than 100 Ω.
• Small variation in h FE (say 50 to 150) that indicates tight control of VBE characteristics. Transistors such as 2N3904, 2N3906, or equivalents in SOT-23 packages are suitable devices to use. THERMAL INERTIA AND SELF-HEATING Accuracy depends on the temperature of the remote-sensing diode and/or the internal temperature sensor being at the same temperature as that being measured, and a number of factors can affect this. Ideally, the sensor should be in good thermal contact with the part of the system being measured, for example the processor. If it is not, the thermal inertia caused by the mass of the sensor will cause a lag in the response of the sensor to a temperature change. In the case of the remote sensor this should not be a problem, as it will either be a substrate transistor in the processor, or can be a small package device such as SOT-23 placed in close proximity to it. The on-chip sensor, however, will often be remote from the processor, and will only be monitoring the general ambient temperature around the package. The thermal time constant of the SO-8 package in still air is about 140 seconds, and if the ambient air temperature quickly changed by 100 degrees, it would take about 12 minutes (5 time constants) for the junction temperature of the ADM1032 to settle within 1 degree of this. In practice, the ADM1032 package will be in electrical, and hence thermal, contact with a printed circuit board, and may also be in a forced airflow. How accurately the temperature of the board and/or the forced airflow reflect the temperature to be measured will also affect the accuracy. Self-heating due to the power dissipated in the ADM1032 or the remote sensor, causes the chip temperature of the device or remote sensor to rise above ambient. However, the current forced through the remote sensor is so small that self-heating is neglig ible. In the case of the ADM1032, the worst-case condition occurs when the device is converting at 16 conversions per second while sinking the maximum current of 1 mA at the ALERT and THERM output. In this case, the total power dissipation in the device is about 11 mW. The thermal resistance, θJA, of the SO-8 package is about 121°C/W. In practice, the package will have electrical and hence thermal connection to the printed circuit board, so the temperature rise due to self-heating will be negligible. LAYOUT CONSIDERATIONS Digital boards can be electrically noisy environments, and the ADM1032 is measuring very small voltages from the remote sensor, so care must be taken to minimize noise induced at the sensor inputs. The following precautions should be taken: Place the ADM1032 as close as possible to the remote sensing diode. Provided that the worst noise sources, i.e., clock gen- erators, data/address buses, and CRTs, are avoided, this distance can be 4 to 8 inches. 2. Route the D+ and D – tracks close together, in parallel, with grounded guard tracks on each side. Provide a ground plane under the tracks if possible. 3. Use wide tracks to minimize inductance and reduce noise pickup. 10 mil track minimum width and spacing is recommended. 10MIL 10MIL 10MIL 10MIL 10MIL 10MIL 10MIL GND GND

Figure 6. Arrangement of Signal Tracks

1. Try to minimize the number of copper/solder joints, which

and at the same temperature.