View ADM1020_82472.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

a
FEATURES 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 SMBusTM Serial Interface Supports SMBus Alert 70 A Max Operating Current 3 A Standby Current +3 V to +5.5 V Supply 8-Lead SOIC Package APPLICATIONS Desktop Computers Notebook Computers Smart Batteries Industrial Controllers Telecommunication Equipment Instrumentation
8-Lead, Low-Cost, System Temperature Monitor ADM1020
PRODUCT DESCRIPTION
The ADM1020 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 NPN or 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 device such as the 2N3904. 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 ADM1020 communicates over a two-wire serial interface compatible with System Management Bus (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 ON-CHIP TEMP. SENSOR D+ D- LOCAL TEMPERATURE VALUE REGISTER LOCAL TEMPERATURE LOW LIMIT COMPARATOR LOCAL TEMPERATURE HIGH LIMIT COMPARATOR REMOTE TEMPERATURE LOW LIMIT COMPARATOR REMOTE TEMPERATURE HIGH LIMIT COMPARATOR LOCAL TEMPERATURE LOW LIMIT REGISTER LOCAL TEMPERATURE HIGH LIMIT REGISTER REMOTE TEMPERATURE LOW LIMIT REGISTER REMOTE TEMPERATURE HIGH LIMIT REGISTER CONFIGURATION REGISTER EXTERNAL DIODE OPEN-CIRCUIT STATUS REGISTER INTERRUPT MASKING ALERT
ANALOG MUX
8-BIT A-TO-D CONVERTER BUSY RUN/STANDBY REMOTE TEMPERATURE VALUE REGISTER
ADM1020
SMBUS INTERFACE
VDD
GND
SDATA
SCLK
ADD
SMBus is a trademark of Intel Corporation. Pentium is a registered trademark of Intel Corporation.
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 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., 1999
ADM1020-SPECIFICATIONS (T = T
A
MIN to T MAX,
VDD = 3.0 V to 3.6 V, unless otherwise noted)
Max Units C C C C C V V mV V mV A A A A ms A A V A Test Conditions/Comments Guaranteed No Missed Codes
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
Min 1 -3 -3 -5 3 2.5
Typ
1 +3 +3 +5 3.6 2.95
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
2.7 25 1.7 50 3 4 70 160 115
0.9
2.2 10 190 290 170
65
D- Source Voltage Address Pin Bias Current 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
90 5.5 0.7 50
2.2 0.8 6 1 -1 5 0 4.7 4 4.7 250 4 4 250 0 4.7 1 100
V V mA mA A pF kHz s s s ns s s ns s s s
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
+1
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
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.
-2-
REV. 0
ADM1020
ABSOLUTE MAXIMUM RATINGS* PIN FUNCTION DESCRIPTION
Positive Supply Voltage (VDD ) to GND . . . . . . . . -0.3 V, +6 V D+, ADD . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V, VDD + 0.3 V D- to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . .-0.3 V, +0.6 V SCLK, SDATA, ALERT . . . . . . . . . . . . . . . . . . . . . -0.3 V, +6 V Input Current, SDATA . . . . . . . . . . . . . . . . . . . . . -1, 50 mA Input Current, D- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 mA ESD Rating, all Pins (Human Body Model) . . . . . . . . 4000 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.
Pin No. 1 2 3 4 5 6 7 8
Mnemonic VDD D+ D- ADD GND ALERT SDATA SCLK
Description Positive Supply, +3 V to +5.5 V Positive Connection to Emitter of Remote Temperature Sensor. Negative Connection to Base of Remote Temperature Sensor. Address Select Three-State Logic Input. Supply 0 V Connection. Open-Drain Logic Output Used as Interrupt or SMBus Alert. Logic Input/Output, SMBus Serial Data. Open-Drain Output. Logic Input, SMBus Serial Clock.
PIN CONFIGURATION
VDD 1 D+ 2
8
THERMAL CHARACTERISTICS
SCLK
8-Lead SOIC Package: JA = 150C/Watt.
SDATA TOP VIEW D- 3 (Not to Scale) 6 ALERT ADD 4 5 GND
7
ADM1020
ORDERING GUIDE Temperature Range 0C to +85C Package Description 8-Lead Small Outline (SOIC) Package Option SO-8
Model* ADM1020AR-REEL ADM1020AR-REEL7
*REEL contains 2500 pieces; REEL7 contains 1000 pieces.
REV. 0
-3-
ADM1020 -Typical Performance Characteristics
30 20 90 TEMPERATURE ERROR - C 10 D+ TO GND 0 READING -10 D+ TO VCC (5V) -20 -30 -40 -50 -60 1.0 3.3 10 30 LEAKAGE RESISTANCE - M 100 80 70 60 50 40 30 20 10 0 0 10 20 60 70 80 30 40 50 MEASURED TEMPERATURE 90 100 110 120 100
Figure 1. Temperature Error vs. PC Board Track Resistance
Figure 4. Pentium II Temperature Measurement vs. ADM1020 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 50
0
500
5k
500k 50k FREQUENCY - Hz
5M
50M
-5 1.0
2.2
3.2 4.7 D+ AND D- CAPACITANCE - nF
7
10
Figure 2. Temperature Error vs. Power Supply Noise Frequency
Figure 5. Temperature Error vs. Capacitance Between D+ and D-
25
80 70
20 TEMPERATURE ERROR - C 100mV p-p 15 SUPPLY CURRENT - A 10 50mV p-p 5 60 50 40 VCC = +5V 30 20 10 -5 50 0 500 5k 50k 500k FREQUENCY - Hz 5M 50M 0 1k 5k 10k 25k 50k 75k 100k 250k 500k 750k 1M SCLK FREQUENCY - Hz VCC = +3V
0
25mV p-p
Figure 3. Temperature Error vs. Common-Mode Noise Frequency
Figure 6. Standby Supply Current vs. Clock Frequency
-4-
REV. 0
ADM1020
10 9 TEMPERATURE ERROR - C 8 7 10mV SQ. WAVE 6 5 4 3 2 0 1 0 50 500 5k 100k 50k 500k FREQUENCY - Hz 5M 25M 50M -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 A 80 100 ADDX = HI-Z
SUPPLY CURRENT -
60
40 ADDX = GND 20
Figure 7. Temperature Error vs. Differential-Mode Noise Frequency
200 180 160 A SUPPLY CURRENT - 140 120 100 80 60 40 20 0 0.0625 VCC = +5V VCC = +3.3V
Figure 9. Standby Supply Current vs. Supply Voltage
125
100 TEMPERATURE - C
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 8. Operating Supply Current vs. Conversion Rate
FUNCTIONAL DESCRIPTION
Figure 10. Response to Thermal Shock
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
The ADM1020 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 ADM1020 is operating normally, the A-to-D converter operates in a free-running 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 (SMBus). The contents of any register can also be read back via the SMBus.
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 ADM1020 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. -5-
REV. 0
ADM1020
VDD I N I IBIAS LOWPASS FILTER fC = 65kHz
D+ REMOTE SENSING TRANSISTOR C1* D-
VOUT+ TO ADC VOUT-
BIAS DIODE
*CAPACITOR C1 IS OPTIONAL. IT IS ONLY NECESSARY IN NOISY ENVIRONMENTS. C1 = 2.2nF TYPICAL, 3nF MAX.
Figure 11. Input Signal Conditioning
Figure 11 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, hence to a chopper-stabilized 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
ADM1020 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 ADM1020 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 ADM1020'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 0F 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, or require, an address, as it is the register to which the first data byte of every write operation is automatically written. 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.
-6-
REV. 0
ADM1020
The power-on default value of the Address Pointer Register is 00h, so if a read operation is performed immediately after poweron, 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 ADM1020 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 are 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 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 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 0F Not Applicable 13 14 16 18 Not Applicable 21 Not Applicable Not Applicable
Name Address Pointer Local Temperature Value Remote Temperature Value Status Configuration Conversion Rate Local Temperature High Limit Local Temperature Low Limit Remote Temperature High Limit Remote Temperature Low Limit One-Shot Reserved Reserved Reserved Reserved Reserved Reserved Reserved Manufacturer ID Die Revision Code
Power-On Default Undefined 0000 0000 (00h) 0000 0000 (00h) Undefined 0000 0000 (00h) 0000 0010 (02h) 0111 1111 (7Fh) (127C) 1100 1001 (C9h) (-55C) 0111 1111 (7Fh) (127C) 1100 1001 (C9h) (-55C) See Note 1 Undefined (Note 2) Undefined (Note 2) Undefined (Note 2) 1000 0000 (Note 2) Undefined (Note 2) 0000 0000 (Note 2) Undefined 0100 0001 (41h) Undefined
NOTES 1 Writing to address 0F causes the ADM1020 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.
REV. 0
-7-
ADM1020
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
same bus, and/or to avoid conflict with other devices. Although only one address pins is provided, it is a three-level input, and can be grounded, left unconnected, or tied to VDD, so that a total of three different addresses are possible, as shown in Table VI. It should be noted that the state of the address pin is only sampled at power-up, so changing it after power-up will have no effect.
Table VI. Device Addresses
Conversion Rate Register
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
ADD 0 NC 1
Device Address 1001 100 1001 101 1001 110
NOTE: ADD is sampled at power-up only.
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 a 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, 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 9th 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. 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.
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
Limit Registers
The ADM1020 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 with 80C, then 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 ADM1020 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 oneshot conversion. The data written to this address is irrelevant and is not stored.
SERIAL BUS INTERFACE
Control of the ADM1020 is carried out via the serial bus. The ADM1020 is connected to this bus as a slave device, under the control of a master device, e.g., the PIIX4
ADDRESS PIN
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 ADM1020 has an address select pin, ADD to allow selection of the device address, so that more than one ADM1020 can be used on the -8-
REV. 0
ADM1020
In the case of the ADM1020, 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, then 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 12a. 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 ADM1020'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 ADM1020 as before, but only the data byte containing the
1 SCLK 9
register read address is sent, as data is not to be written to the register. This is shown in Figure 12b. 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 12c. 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 12b 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 ADM1020 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 9
SDATA START BY MASTER
A6
A5
A4
A3
A2
A1
A0
R/W ACK. BY ADM1020
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY ADM1020
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 ADM1020 MASTER
FRAME 3 DATA BYTE
Figure 12a. Writing a Register Address to the Address Point 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 ADM1020
D7
D6
D5
D4
D3
D2
D1
D0 ACK. BY ADM1020 STOP BY MASTER
FRAME 1 SERIAL BUS ADDRESS BYTE
FRAME 2 ADDRESS POINTER REGISTER BYTE
Figure 12b. Writing to the Address Pointer Register Only
1 SCLK 9 1 9
SDATA START BY MASTER
A6
A5
A4
A3
A2
A1
A0
R/W ACK. BY ADM1020
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 ADM1020
Figure 12c. Reading Data from a Previously Selected Register
REV. 0
-9-
ADM1020
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 not normally 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 13.
MASTER RECEIVES SMBALERT START ALERT RESPONSE ADDRESS MASTER SENDS ARA AND READ COMMAND RD ACK DEVICE ADDRESS DEVICE SENDS ITS ADDRESS NO ACK STOP
ALERT OUTPUT
SENSOR FAULT DETECTION
The ADM1020 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 -128 (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 ADM1020 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, the resulting ALERT may be cleared by writing 80h (-128C) to the low limit register.
Figure 13 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 ADM1020 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.
LOW POWER STANDBY MODES
APPLICATIONS INFORMATION
FACTORS AFFECTING ACCURACY Remote Sensing Diode
The ADM1020 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.
The ADM1020 can be put into a low power standby mode by setting Bit 6 of the Configuration Register. With Bit 6 low the ADM1020 operates normally. When 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. When Bit 6 is set , a one-shot conversion of both channels can be initiated by writing XXh to the One-Shot Register (address 0Fh).
-10-
REV. 0
ADM1020
LAYOUT CONSIDERATIONS
Digital boards can be electrically noisy environments, and the ADM1020 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 ADM1020 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 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.
GND 10mil 10mil D+ 10mil 10mil D- 10mil 10mil GND 10mil
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 ADM1020. 6. If the distance to the remote sensor is more than 8 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 ADM1020. 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.
APPLICATION CIRCUITS
Figure 15 shows a typical application circuit for the ADM1020, 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.
VDD 0.1 F +3.3V 10k 10k 10k IN I/O OUT SET TO REQUIRED ADDRESS TO PIIX4 CHIP
Figure 14. 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 should not be a major problem as 1C corresponds to about 200 mV, and thermocouple voltages are about 3 mV/C of temperature difference. Unless there are two thermocouples with a big temperature differential between them, thermocouple voltages should be much less than 200 mV.
ADM1020
D+ C1* D- 2N3904 SHIELD ALERT ADD *C1 IS OPTIONAL GND SDATA SCLK
Figure 15. Typical ADM1020 Application Circuit
REV. 0
-11-
ADM1020
The SCLK, and SDATA pins of the ADM1020 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 16 shows how the ADM1020 might be integrated into a system using this type of I/O controller.
PROCESSOR
BUILT-IN SENSOR PCI SLOTS
HOST BUS
SECOND LEVEL CACHE
HOST-TO-PCI BRIDGE
MAIN MEMORY (DRAM)
PCI BUS (3.3V OR 5V 30/33MHz) HARD DISK USB PORT 1 BMI IDE ULTRA DMA/33 HARD DISK 8237 1AB (PIIX4) USB PORT 2 GPI [ I,O] (30+)
CD ROM
D-
D+
ADM1020
ALERT SCLK SDATA SERIAL PORT PARALLEL PORT FLOPPY DISK CONTROLLER INFRARED
SMBUS ISA/EIO BUS (3.3V, 5V TOLERANT)
AUDIO
KEYBOARD
BIOS
Figure 16. Typical System Using ADM1020
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead SOIC (SO-8)
0.1968 (5.00) 0.1890 (4.80)
8 5 4
0.1574 (4.00) 0.1497 (3.80) PIN 1
1
0.2440 (6.20) 0.2284 (5.80)
0.0500 (1.27) BSC 0.0098 (0.25) 0.0040 (0.10) SEATING PLANE 0.0688 (1.75) 0.0532 (1.35) 0.0192 (0.49) 0.0138 (0.35) 8 0.0098 (0.25) 0 0.0075 (0.19)
0.0196 (0.50) 0.0099 (0.25)
45
0.0500 (1.27) 0.0160 (0.41)
-12-
REV. 0
PRINTED IN U.S.A.
C3445-4-4/99

▲Up To Search▲

Price & Availability of ADM1020

	To Download ADM1020 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .