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FEATURES Improved Replacement for MAX1617 On-Chip and Remote Temperature Sensing No Calibration Necessary 1 C Accuracy for On-Chip Sensor 3 C Accuracy for Remote Sensor Programmable Over/Under Temperature Limits Programmable Conversion Rate 2-Wire SMBus Serial Interface Supports System Management Bus (SMBusTM) Alert 70 A Max Operating Current 3 A Standby Current 3 V to 5.5 V Supply Small 16-Lead QSOP Package APPLICATIONS Desktop Computers Notebook Computers Smart Batteries Industrial Controllers Telecomms Equipment Instrumentation
Low Cost Microprocessor System Temperature Monitor ADM1021
PRODUCT DESCRIPTION
The ADM1021 is a two-channel digital thermometer and under/ over temperature alarm, intended for use in personal computers and other systems requiring thermal monitoring and management. The device can measure the temperature of a microprocessor using a diode-connected PNP transistor, which may be provided on-chip in the case of the Pentium(R) II or similar processors, or can be a low cost discrete NPN/PNP device such as the 2N3904/2N3906. 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 measures the output of an on-chip temperature sensor, to monitor the temperature of the device and its environment. The ADM1021 communicates over a two-wire serial interface compatible with SMBus standards. Under and over temperature limits can be programmed into the devices over the serial bus, and an ALERT output signals when the on-chip or remote temperature is out of range. This output can be used as an interrupt, or as an SMBus alert.
FUNCTIONAL BLOCK DIAGRAM
ADDRESS POINTER REGISTER ONE-SHOT REGISTER CONVERSION RATE REGISTER
LOCAL TEMPERATURE VALUE REGISTER LOCAL TEMPERATURE LOW LIMIT COMPARATOR LOCAL TEMPERATURE HIGH LIMIT COMPARATOR ANALOG MUX LOCAL TEMPERATURE LOW LIMIT REGISTER
ON-CHIP TEMP. SENSOR
D+ D-
LOCAL TEMPERATURE HIGH LIMIT REGISTER REMOTE TEMPERATURE LOW LIMIT REGISTER REMOTE TEMPERATURE HIGH LIMIT REGISTER
8-BIT A-TO-D CONVERTER
BUSY RUN/STANDBY REMOTE TEMPERATURE LOW LIMIT COMPARATOR REMOTE TEMPERATURE HIGH LIMIT COMPARATOR
REMOTE TEMPERATURE VALUE REGISTER
CONFIGURATION REGISTER
EXTERNAL DIODE OPEN-CIRCUIT STATUS REGISTER
STBY
INTERRUPT MASKING
ALERT
ADM1021
SMBUS INTERFACE
TEST
VDD
NC
GND
GND
NC
NC
TEST
SDATA
SCLK
ADD0
ADD1
SMBus is a trademark and Pentium is a registered trademark of Intel Corporation.
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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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 (c) Analog Devices, Inc., 1998
ADM1021-SPECIFICATIONS
Parameter POWER SUPPLY AND ADC Temperature Resolution Temperature Error, Local Sensor Temperature Error, Remote Sensor Supply Voltage Range Undervoltage Lockout Threshold Undervoltage Lockout Hysteresis Power-On Reset Threshold POR Threshold Hysteresis Standby Supply Current Average Operating Supply Current Auto-Convert Mode, Averaged Over 4 Seconds Conversion Time Remote Sensor Source Current 1
(TA = TMIN to TMAX, VDD = 3.0 V to 3.6 V, unless otherwise noted)
Typ Max Units C C C C C V V mV V mV A A A A ms A A V A V 0.8 V mA mA A pF kHz s s s ns s s ns s s s Test Conditions/Comments Guaranteed No Missed Codes
Min
1 +3 +3 +5 3.6 2.95
-3 -3 -5 3 2.5
TA = +60C to +100C Note 1 VDD Input, Disables ADC, Rising Edge VDD, Falling Edge2 VDD = 3.3 V, No SMBus Activity SCLK at 10 kHz 0.25 Conversions/Sec Rate 2 Conversions/Sec Rate From Stop Bit to Conversion Complete (Both Channels) D+ Forced to D- + 0.65 V High Level Low Level Momentary at Power-On Reset VDD = 3 V to 5.5 V VDD = 3 V to 5.5 V SDATA Forced to 0.6 V ALERT Forced to 0.4 V
2.7 25 1.7 50 3 4 70 160 115
0.9
2.2 10 90 200 170
65
60 3.5 D-Source Voltage Address Pin Bias Current (ADD0, ADD1) SMBUS INTERFACE Logic Input High Voltage, VIH STBY, SCLK, SDATA Logic Input Low Voltage, VIL STBY, SCLK, SDATA SMBus Output Low Sink Current ALERT Output Low Sink Current Logic Input Current, IIH, IIL SMBus Input Capacitance, SCLK, SDATA SMBus Clock Frequency SMBus Clock Low Time, tLOW SMBus Clock High Time, tHIGH SMBus Start Condition Setup Time, tSU:STA SMBus Repeat Start Condition Setup Time, tSU:STA SMBus Start Condition Hold Time, tHD:STA SMBus Stop Condition Setup Time, tSU:STO SMBus Data Valid to SCLK Rising Edge Time, tSU:DAT SMBus Data Hold Time, tHD:DAT SMBus Bus Free Time, tBUF SCLK Falling Edge to SDATA Valid Time, tVD,DAT 2.2
90 5.5 0.7 50
130 8
6 1 -1 5 0 4.7 4 4.7 250 4 4 250 0 4.7
+1 100
tLOW Between 10% Points tHIGH Between 90% Points Between 90% and 90% Points Time from 10% of SDATA to 90% of SCLK Time from 90% of SCLK to 10% of SDATA Time from 10% or 90% of SDATA to 10% of SCLK Between Start/Stop Condition Master Clocking in Data
1
NOTES 1 Operation at VDD = +5 V guaranteed by design, not production tested. 2 Guaranteed by design, not production tested. Specifications subject to change without notice.
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ABSOLUTE MAXIMUM RATINGS*
PIN FUNCTION DESCRIPTIONS Pin No. 1, 16 2 3 4 5, 9, 13 6 7, 8 10 11 12 14 15 Mnemonic TEST VDD D+ D- NC ADD1 GND ADD0 ALERT SDATA SCLK STBY Description Test pin for factory use only. See note. Positive supply, +3 V to +5.5 V. Positive connection to remote temperature sensor. Negative connection to remote temperature sensor. No Connect. Three-state logic input, higher bit of device address. Supply 0 V connection. Three-state logic input, lower bit of device address. Open-drain logic output used as interrupt or SMBus alert. Logic input/output, SMBus serial data. Open-drain output. Logic input, SMBus serial clock. Logic input selecting normal operation (high) or standby mode (low).
Positive Supply Voltage (VDD) to GND . . . . . . . -0.3 V to +6 V D+, ADD0, ADD1 . . . . . . . . . . . . . . . . -0.3 V to VDD + 0.3 V D- to GND . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to +0.6 V SCLK, SDATA, ALERT, STBY . . . . . . . . . . . . -0.3 V to +6 V Input Current, SDATA . . . . . . . . . . . . . . . . -1 mA to +50 mA Input Current, D- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 mA ESD Rating, all pins (Human Body Model) . . . . . . . . 2000 V Continuous Power Dissipation Up to +70C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 650 mW Derating above +70C . . . . . . . . . . . . . . . . . . . . 6.7 mW/C Operating Temperature Range . . . . . . . . . . -55C to +125C Maximum Junction Temperature (TJ max) . . . . . . . . . +150C Storage Temperature Range . . . . . . . . . . . . -65C to +150C Lead Temperature, Soldering Vapor Phase 60 sec . . . . . . . . . . . . . . . . . . . . . . . . . +215C Infrared 15 sec . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +200C
*Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
THERMAL CHARACTERISTICS
16-Lead QSOP Package: JA = 150C/Watt.
ORDERING GUIDE
NOTE Pins 1 and 16 are reserved for test purposes. Ideally these pins should be left unconnected. If routing through these pins is required, then both should be at the same potential (i.e., connected together).
Model
Temperature Range
Package Description
Package Option
PIN CONFIGURATION
TEST 1 VDD 2 D+ 3
16 TEST 15 STBY 14 SCLK
ADM1021ARQ 0C to +85C
16-Lead QSOP RQ-16
PROTOCOL
START CONDITION (S)
BIT 7 MSB (A7)
BIT 6 (A6) 1/fSCL
t LOW
SCL
t HIGH
13 NC TOP VIEW NC 5 (Not to Scale) 12 SDATA
D- 4
ADM1021
ADD1 6 GND 7 GND 8
11 ALERT 10 ADD0 9
NC
tR
SDA
tF
NC = NO CONNECT
PROTOCOL
BIT 0 LSB (R/W)
ACKNOWLEDGE (A)
STOP CONDITION (P)
SCL
SDA
Figure 1. Diagram for Serial Bus Timing
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ADM1021-Typical Performance Characteristics
30 20
90
TEMPERATURE ERROR - C
120 100
10 DXP TO GND 0
READING
80 70 60 50 40
-10 DXP TO VCC (5V) -20 -30 -40 -50 -60 1 10 30 3.3 LEAKAGE RESISTANCE - M 100
30 20 10 0 0 10 20 60 70 80 30 40 50 MEASURED TEMPERATURE 90 100 110
Figure 2. Temperature Error vs. PC Board Track Resistance
Figure 5. Pentium II Temperature Measurement vs. ADM1021 Reading
25
6
5
TEMPERATURE ERROR - C
TEMPERATURE ERROR - C
20
4 250mV p-p REMOTE 3 2
15
10
5
1 100mV p-p REMOTE 0 -1
0
50
500
5k
500k 50k FREQUENCY - Hz
5M
50M
-5
1
2.2
3.2 4.7 DXP-DXN CAPACITANCE - nF
7
10
Figure 3. Temperature Error vs. Power Supply Noise Frequency
Figure 6. Temperature Error vs. Capacitance Between D+ and D-
25
80 70
20
TEMPERATURE ERROR - C
100mV p-p 15
SUPPLY CURRENT - A
60 50 40 VCC = +5V 30 20 10 VCC = +3V
10 50mV p-p 5
0
25mV p-p
-5 50 500 5k 50k 500k FREQUENCY - Hz 5M 50M
0 0 1k 5k 10k 25k 50k 75k 100k 250k 500k 750k 1M SCLK FREQUENCY - Hz
Figure 4. Temperature Error vs. Common-Mode Noise Frequency
Figure 7. Standby Supply Current vs. Clock Frequency
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10 9
100 ADDX = HI-Z 80
A
10mV SQ. WAVE
TEMPERATURE ERROR - C
8 7 6 5 4 3 2 1 0 50 500 5k 50k 100k 500k FREQUENCY - Hz 5M 25M 50M
SUPPLY CURRENT -
60
40 ADDX = GND 20
0
-20
0
1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.5 4.5 SUPPLY VOLTAGE - Volts
Figure 8. Temperature Error vs. Differential-Mode Noise Frequency
200 180 160
Figure 10. Standby Supply Current vs. Supply Voltage
125
100
SUPPLY CURRENT - A
TEMPERATURE - C
140 120 100 80 60 40 20 0 0.0625 VCC = +5V VCC = +3.3V
75
50
25
IMMERSED IN +115 C FLUORINERT BATH
0
0.125 0.25 0.5 1 2 CONVERSION RATE - Hz 4 8
T=0
T=2
T=4 TIME - Sec
T=6
T=8
T = 10
Figure 9. Operating Supply Current vs. Conversion Rate
FUNCTIONAL DESCRIPTION
Figure 11. Response to Thermal Shock
The ADM1021 contains a two-channel A-to-D converter with special input-signal conditioning to enable operation with remote and on-chip diode temperature sensors. When the ADM1021 is operating normally, the A-to-D converter operates in a freerunning mode. The analog input multiplexer alternately selects either the on-chip temperature sensor to measure its local temperature, or the remote temperature sensor. These signals are digitized by the ADC and the results stored in the Local and Remote Temperature Value Registers as 8-bit, twos complement words. The measurement results are compared with Local and Remote, High and Low Temperature Limits, stored in four on-chip registers. Out-of-limit comparisons generate flags that are stored in the status register, and one or more out-of-limit results will cause the ALERT output to pull low. The limit registers can be programmed, and the device controlled and configured, via the serial System Management Bus. The contents of any register can also be read back via the SMBus.
Control and configuration functions consist of: * Switching the device between normal operation and standby mode. * Masking or enabling the ALERT output. * Selecting the conversion rate.
MEASUREMENT METHOD
A simple method of measuring temperature is to exploit the negative temperature coefficient of a diode, or the base-emitter voltage of a transistor, operated at constant current. Unfortunately, this technique requires calibration to null out the effect of the absolute value of Vbe, which varies from device to device. The technique used in the ADM1021 is to measure the change in Vbe when the device is operated at two different currents. This is given by: Vbe = KT/q x ln (N) where: K is Boltzmann's constant q is charge on the electron (1.6 x 10-19 Coulombs) T is absolute temperature in Kelvins N is ratio of the two currents
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ADM1021
VDD I N I IBIAS
D+ REMOTE SENSING TRANSISTOR C1* D- BIAS DIODE LOWPASS FILTER fC = 65kHz
VOUT+ TO ADC VOUT-
* CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 2.2nF TYPICAL, 3nF MAX.
Figure 12. Input Signal Conditioning
Figure 12 shows the input signal conditioning used to measure the output of an external temperature sensor. This figure shows the external sensor as a substrate transistor, provided for temperature monitoring on some microprocessors, but it could equally well be a discrete transistor. If a discrete transistor is used, the collector will not be grounded and should be linked to the base. To prevent ground noise interfering with the measurement, the more negative terminal of the sensor is not referenced to ground, but is biased above ground by an internal diode at the D- input. If the sensor is operating in a noisy environment, C1 may optionally be added as a noise filter. Its value is typically 2200 pF, but should be no more than 3000 pF. See the section on layout considerations for more information on C1. To measure Vbe, the sensor is switched between operating currents of I and N x I. The resulting waveform is passed through a 65 kHz low-pass filter to remove noise, thence to a chopperstabilized amplifier that performs the functions of amplification and rectification of the waveform to produce a dc voltage proportional to Vbe. This voltage is measured by the ADC to give a temperature output in 8-bit twos complement format. To further reduce the effects of noise, digital filtering is performed by averaging the results of 16 measurement cycles. Signal conditioning and measurement of the internal temperature sensor is performed in a similar manner.
TEMPERATURE DATA FORMAT
Table I. Temperature Data Format
Temperature -128C -125C -100C -75C -50C -25C -1C 0C +1C +10C +25C +50C +75C +100C +125C +127C
REGISTERS
Digital Output 1 000 0000 1 000 0011 1 001 1100 1 011 0101 1 100 1110 1 110 0111 1 111 1111 0 000 0000 0 000 0001 0 000 1010 0 001 1001 0 011 0010 0 100 1011 0 110 0100 0 111 1101 0 111 1111
One LSB of the ADC corresponds to 1C, so the ADC can theoretically measure from -128C to +127C, although the practical lowest value is limited to -65C due to device maximum ratings. The temperature data format is shown in Table I. The results of the local and remote temperature measurements are stored in the local and remote temperature value registers, and are compared with limits programmed into the local and remote high and low limit registers.
The ADM1021 contains nine 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 II to IV. It should be noted that the ADM1021's registers are dual port, and have different addresses for read and write operations. Attempting to write to a read address, or to read from a write address, will produce an invalid result. Register addresses above 0Fh are reserved for future use or used for factory test purposes and should not be written to.
Address Pointer Register
The Address Pointer Register itself does not have, nor does it 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.
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The power-on default value of the Address Pointer 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 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.
Table II. Status Register Bit Assignments
The ADM1021 has two registers to store the results of Local and Remote temperature measurements. These registers are written to by the ADC and can only be read over the SMBus.
Status Register
Bit 7 6 5 4 3 2 1-0
Name BUSY LHIGH* LLOW* RHIGH* RLOW* OPEN*
Function 1 When ADC Converting. 1 When Local High Temp Limit Tripped. 1 When Local Low Temp Limit Tripped. 1 When Remote High Temp Limit Tripped. 1 When Remote Low Temp Limit Tripped. 1 When Remote Sensor Open-Circuit. Reserved.
Bit 7 of the Status Register indicates that the ADC is busy converting when it is high. Bits 5 to 3 are flags that indicate the results of the limit comparisons. If the local and/or remote temperature measurement is above the corresponding high temperature limit or below the corresponding low temperature limit, then one or more of these flags will be set. Bit 2 is a flag that is set if the remote temperature sensor is open-circuit. These five flags are 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-oflimit measurement, or the sensor is open-circuit, the corresponding flag bit cannot be reset. A flag bit can only be reset if the corresponding value register contains an in-limit measurement, or the sensor is good.
*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. Standby mode can also be selected by taking the STBY pin low. 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 ALERT output is enabled. If Bit 7 is set to 1, the ALERT output is disabled.
Table III. List of ADM1021 Registers
READ Address (Hex) Not Applicable 00 01 02 03 04 05 06 07 08 Not Applicable 10 11 12 15 17 19 20 FE FF
WRITE Address (Hex) Not Applicable Not Applicable Not Applicable Not Applicable 09 0A 0B 0C 0D 0E 0F1 Not Applicable 13 14 16 18 Not Applicable 21 Not Applicable Not Applicable
Name Address Pointer Local Temp. Value Remote Temp. Value Status Configuration Conversion Rate Local Temp. High Limit Local Temp. Low Limit Remote Temp. High Limit Remote Temp. Low Limit One-Shot Reserved Reserved Reserved Reserved Reserved Reserved Reserved Manufacturer Device ID Die Revision Code
Power-On Default Undefined 0000 0000 0000 0000 Undefined 0000 0000 0000 0010 0111 1111 1100 1001 0111 1111 1100 1001 (00h) (00h) (00h) (02h) (7Fh) (+127C) (C9h) (-55C) (7Fh) (+127C) (C9h) (-55C)
Undefined2 Undefined2 Undefined2 1000 00002 Undefined2 0000 00002 Undefined 0100 0001 (41h) Undefined
NOTES 1 Writing to address 0F causes the ADM1021 to perform a single measurement. It is not a data register as such and it does not matter what data is written to it. 2 These registers are reserved for future versions of the device.
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Table IV. Configuration Register Bit Assignments
Bit 7 6 5-0
Name MASK1 RUN/STOP
Function 0 = ALERT Enabled 1 = ALERT Masked 0 = Run 1 = Standby Reserved
Power-On Default 0 0 0
device address, so that several ADM1021s can be used on the same bus, and/or to avoid conflict with other devices. Although only two address pins are provided, these are three-state, and can be grounded, left unconnected, or tied to VDD, so that a total of nine different addresses are possible, as shown in Table VI. It should be noted that the state of the address pins is only sampled at power-up, so changing them after power-up will have no effect.
Table VI. Device Addresses
Conversion Rate Register
ADD0 0 0 0 NC NC NC 1 1 1
ADD1 0 NC 1 0 NC 1 0 NC 1
Device Address 0011 000 0011 001 0011 010 0101 001 0101 010 0101 011 1001 100 1001 101 1001 110
The lowest three bits of this register are used to program the conversion rate by dividing the ADC clock by 1, 2, 4, 8, 16, 32, 64 or 128, to give conversion times from 125 ms (Code 07h) to 16 seconds (Code 00h). This register can be written to and read back over the SMBus. The higher five 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 V.
Table V. Conversion Rate Register Codes
Note: ADD0, ADD1 sampled at power-up only.
Data 00h 01h 02h 03h 04h 05h 06h 07h 08h to FFh
Conversion/sec 0.0625 0.125 0.25 0.5 1 2 4 8 Reserved
Average Supply Current A Typ at VCC = 3.3 V 42 42 42 48 60 82 118 170
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, consisting 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 Acknowledge Bit. All other devices on the bus now remain idle while the selected device waits for data to be read from or written to it. If the R/W bit is a 0, then 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 conditions are established. In WRITE mode, the master will pull the data line high during the 10th 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 10th clock pulse, then high during the 10th clock pulse to assert a STOP condition.
Limit Registers
The ADM1021 has four limit registers to store local and remote, high and low 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 as a limit of 80C, measuring 81C will result in an alarm condition.
One-Shot Register
The one-shot register is used to initiate a single conversion and comparison cycle when the ADM1021 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 irrelevant and is not stored.
SERIAL BUS INTERFACE
Control of the ADM1021 is carried out via the serial bus. The ADM1021 is connected to this bus as a slave device, under the control of a master device, e.g., the PIIX4.
ADDRESS PINS
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 ADM1021 has two address pins, ADD0 and ADD1, to allow selection of the -8-
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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 ADM1021, write operations contain either one or two bytes, while read operations contain one byte and perform 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 13. 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 ADM1021'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 ADM1021 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 14. 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 15. 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, so Figure 14 can be omitted. NOTES 1. Although it is possible to read a data byte from a data register without first writing to the Address Pointer Register, if the Address Pointer Register is already at the correct value, it is not possible to write data to a register without writing to the Address Pointer Register, because the first data byte of a write is always written to the Address Pointer Register. 2. Don't forget that the ADM1021 registers have different addresses for read and write operations. The write address of a register must be written to the Address Pointer if data is to be written to that register, but it is not possible to read data from that address. The read address of a register must be written to the Address Pointer before data can be read from that register.
1 SCLK 9 1 9
SDATA START BY MASTER
A6
A5
A4
A3
A2
A1
A0
R/W ACK. BY ADM1021
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY ADM1021
FRAME 1 SERIAL BUS ADDRESS BYTE 1 SCL (CONTINUED)
FRAME 2 ADDRESS POINTER REGISTER BYTE 9
SDA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY STOP BY ADM1021 MASTER
FRAME 3 DATA BYTE
Figure 13. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
1 SCLK
9
1
9
SDATA START BY MASTER
A6
A5
A4
A3
A2
A1
A0
R/W ACK. BY ADM1021
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY ADM1021 STOP BY MASTER
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 ADDRESS POINTER REGISTER BYTE
Figure 14. Writing to the Address Pointer Register Only
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1 SCLK 9 1 9
SDATA START BY MASTER
A6
A5
A4
A3
A2
A1
A0
R/W ACK. BY ADM1021
D7
D6
D5
D4
D3
D2
D1
D0 NO ACK. STOP BY BY MASTER MASTER
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 DATA BYTE FROM ADM1021
Figure 15. Reading Data from a Previously Selected Register
ALERT OUTPUT LOW POWER STANDBY MODES
The ALERT output goes low whenever an out-of limit measurement is detected, or if the remote temperature sensor is opencircuit. It is an open-drain and requires a 10 k pull-up to VDD. Several ALERT outputs can be wire-ANDED together, so that the common line will go low if one or more of the ALERT outputs goes low. The ALERT output can be used as an interrupt signal to a processor, or it may be used as an SMBALERT. Slave devices on the SMBus can normally not signal to the master that they want to talk, but the SMBALERT function allows them to do so. One or more ALERT outputs are connected to a common SMBALERT line connected to the master. When the SMBALERT line is pulled low by one of the devices, the following procedure occurs as illustrated in Figure 16.
MASTER RECEIVES SMBALERT START ALERT RESPONSE ADDRESS MASTER SENDS ARA AND READ COMMAND RD ACK DEVICE ADDRESS NO ACK STOP
The ADM1021 can be put into a low power standby mode using hardware or software, that is by taking the STBY input low, or by setting Bit 6 of the Configuration Register. When STBY is high, or Bit 6 is low, the ADM1021 operates normally. When STBY is pulled low or Bit 6 is high, the ADC is inhibited, any conversion in progress is terminated without writing the result to the corresponding value register. The SMBus is still enabled. Power consumption in the standby mode is reduced to less than 10 A if there is no SMBus activity, or 100 A if there are clock and data signals on the bus. These two modes are similar but not identical. When STBY is low, conversions are completely inhibited. When Bit 6 is set but STBY is high, a one-shot conversion of both channels can be initiated by writing XXh to the One-Shot Register (address 0Fh).
SENSOR FAULT DETECTION
DEVICE SENDS ITS ADDRESS
The ADM1021 has a fault detector at the D+ input that detects if the external sensor diode is open-circuit. This is a simple voltage comparator that trips if the voltage at D+ exceeds VCC - 1 V (typical). The output of this comparator is checked when a conversion is initiated, and sets Bit 2 of the Status Register if a fault is detected. If the remote sensor voltage falls below the normal measuring range, for example due to the diode being short-circuited, the ADC will output -128C (1000 0000). Since the normal operating temperature range of the device only extends down to -55C, this output code should never be seen in normal operation, so it can be interpreted as a fault condition. Since it will be outside the power-on default low temperature limit (-55C) and any low limit that would normally be programmed, a short-circuit sensor will cause an SMBus alert. In this respect, the ADM1021 differs from and improves upon competitive devices that output zero if the external sensor goes short-circuit. These devices can misinterpret a genuine 0C measurement as a fault condition. If the external diode channel is not being used and it is shorted out, then the resulting ALERT may be cleared by writing 80h (-128C) to the low limit register.
Figure 16. Use of SMBALERT
1. SMBALERT pulled low. 2. Master initiates a read operation and sends the Alert Response Address (ARA = 0001 100). This is a general call address that must not be used as a specific device address. 3. The device whose ALERT output is low responds to the Alert Response Address and the master reads its device address. The address of the device is now known and it can be interrogated in the usual way. 4. If more than one device's ALERT output is low, the one with the lowest device address, will have priority, in accordance with normal SMBus arbitration. 5. Once the ADM1021 has responded to the Alert Response Address, it will reset its ALERT output, provided that the error condition that caused the ALERT no longer exists. If the SMBALERT line remains low, the master will send ARA again, and so on until all devices whose ALERT outputs were low have responded.
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ADM1021
APPLICATIONS INFORMATION
FACTORS AFFECTING ACCURACY Remote Sensing Diode
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.
GND 10 mil. 10 mil. D+ 10 mil. 10 mil.
The ADM1021 is designed to work with substrate transistors built into processors, or with discrete transistors. Substrate transistors will generally be PNP types with the collector connected to the substrate. Discrete types can be either PNP or NPN, connected as a diode (base shorted to collector). If an NPN transistor is used then the collector and base are connected to D+ and the emitter to D-. If a PNP transistor is used then the collector and base are connected to D- and the emitter to D+. The user has no choice in the case of substrate transistors, but if a discrete transistor is used the best accuracy will be obtained by choosing devices according to the following criteria: 1. Base-emitter voltage greater than 0.25 V at 6 A, at the highest operating temperature. 2. Base-emitter voltage less than 0.95 V at 100 A, at the lowest operating temperature. 3. Base resistance less than 100 . 4. Small variation in hfe (say 50 to 150) which indicates tight control of Vbe characteristics. Transistors such as 2N3904, 2N3906 or equivalents in SOT-23 package are suitable devices to use.
Thermal Inertia and Self-Heating
D-
10 mil. 10 mil.
GND
10 mil.
Figure 17. Arrangement of Signal Tracks
4. Try to minimize the number of copper/solder joints, which can cause thermocouple effects. Where copper/solder joints are used, make sure that they are in both the D+ and D- path and at the same temperature. Thermocouple effects should not be a major problem as 1C corresponds to about 240 V, and thermocouple voltages are about 3 V/C of temperature difference. Unless there are two thermocouples with a big temperature differential between them, thermocouple voltages should be much less than 240 V. 5. Place a 0.1 F bypass capacitor close to the VDD pin and 2200 pF input filter capacitors across D+, D- close to the ADM1021. 6. If the distance to the remote sensor is more than eight inches, the use of twisted pair cable is recommended. This will work up to about 6 to 12 feet. 7. For really long distances (up to 100 feet), use shielded twisted pair such as Belden #8451 microphone cable. Connect the twisted pair to D+ and D- and the shield to GND close to the ADM1021. Leave the remote end of the shield unconnected to avoid ground loops. Because the measurement technique uses switched current sources, excessive cable and/or filter capacitance can affect the measurement. When using long cables, the filter capacitor may be reduced or removed. Cable resistance can also introduce errors. 1 series resistance introduces about 0.5C error.
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 be either a substrate transistor in the processor or 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 QSOP-16 package is about 10 seconds. 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 ADM1021 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: 1. Place the ADM1021 as close as possible to the remote sensing diode. Provided that the worst noise sources such as clock generators, data/address buses and CRTs are avoided, this distance can be four to eight inches.
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ADM1021
APPLICATION CIRCUITS
Figure 18 shows a typical application circuit for the ADM1021, using a discrete sensor transistor connected via a shielded, twisted pair cable. The pull-ups on SCLK, SDATA and ALERT are required only if they are not already provided elsewhere in the system. The SCLK, and SDATA pins of the ADM1021 can be interfaced directly to the SMBus of an I/O controller such as the Intel PCI ISA IDE Xcelerator (PIIX4) chip type 82371AB. Figure 19 shows how the ADM1021 might be integrated into a system using this type of I/O controller.
ADM1021 VDD
STBY D+ C1* D- 2N3904 SHIELD SCLK SDATA ALERT ADD0 ADD1 GND 0.1 F IN I/O
3.3V ALL 10k
TO PIIX4 CHIP
OUT
*C1 IS OPTIONAL
Figure 18. Typical ADM1021 Application Circuit
PROCESSOR
BUILT-IN SENSOR
MAIN MEMORY (DRAM)
HOST BUS PCI SLOTS SECOND LEVEL CACHE HOST-TO-PCI BRIDGE MAIN MEMORY (DRAM)
PCI BUS (3.3V OR 5V 30/33MHz)
D- D+ CD ROM HARD DISK USB PORT 1 BMI IDE ULTRA DMA/33 HARD DISK 8237 1AB (PIIX4) USB PORT 2 GPI[I,O] (30+) SMBUS ISA/EIO BUS (3.3V, 5V TOLERANT) AUDIO KEYBOARD
ADM1021
ALERT SCLK SDATA SERIAL PORT PARALLEL PORT FLOPPY DISK CONTROLLER INFRARED
BIOS
Figure 19. Typical System Using ADM1021
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
16-Lead Shrink Small Outline Package (RQ-16)
0.197 (5.00) 0.189 (4.80)
16
9
0.157 (3.99) 0.150 (3.81)
1 8
0.244 (6.20) 0.228 (5.79)
PIN 1 0.059 (1.50) MAX
0.069 (1.75) 0.053 (1.35)
0.010 (0.25) 0.004 (0.10)
0.025 (0.64) BSC
8 0 0.012 (0.30) SEATING 0.010 (0.20) 0.008 (0.20) PLANE 0.007 (0.18)
0.050 (1.27) 0.016 (0.41)
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REV. 0
PRINTED IN U.S.A.
C3354-3-7/98
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