a
1C Remote and Local
System Temperature Monitor
ADM1032*
PRODUCT DESCRIPTION
FEATURES
On-Chip and Remote Temperature Sensing
Offset Registers for System Calibration
0.125C Resolution/1C Accuracy on Remote Channel
1C Resolution/3C 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 A Operating Current
5.5 A Standby Current
3 V to 5.5 V Supply
Small 8-Lead SO and Micro_SO Package
The ADM1032 is a dual-channel digital thermometer and
under/over temperature alarm, intended for use in personal
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 measures the output of an on-chip temperature sensor, to monitor
the temperature of the device and its environment.
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.
APPLICATIONS
Desktop Computers
Notebook Computers
Smart Batteries
Industrial Controllers
Telecomms Equipment
Instrumentation
Embedded Systems
FUNCTIONAL BLOCK DIAGRAM
ADDRESS POINTER
REGISTER
CONVERSION RATE
REGISTER
ON-CHIP
TEMPERATURE
SENSOR
A-TO-D
CONVERTER
BUSY
RUN/STANDBY
LOCAL TEMPERATURE
HIGH-LIMIT REGISTER
LIMIT
COMPARATOR
REMOTE TEMPERATURE
VALUE REGISTER
DIGITAL MUX
D–
ANALOG
MUX
DIGITAL MUX
D+
LOCAL TEMPERATURE
LOW-LIMIT REGISTER
LOCAL TEMPERATURE
VALUE REGISTER
REMOTE TEMPERATURE
LOW-LIMIT REGISTER
REMOTE TEMPERATURE
HIGH-LIMIT REGISTER
LOCAL THERM LIMIT
REGISTER
REMOTE OFFSET
REGISTER
EXTERNAL THERM LIMIT
REGISTER
CONFIGURATION
REGISTER
EXTERNAL DIODE OPEN-CIRCUIT
INTERRUPT
MASKING
STATUS REGISTER
ADM1032
VDD
GND
ALERT
THERM
SMBUS INTERFACE
SDATA
SCLK
Pentium is a registered trademark of Intel Corporation.
*Patents 5,982,221, 6,097,239, 6,133,753, 6,169,442, 5,867,012.
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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., 2001
ADM1032–SPECIFICATIONS (T = T
A
MIN
to TMAX, VDD = VMIN to VMAX, unless otherwise noted.)
Parameter
Min
Typ
Max
Unit
Test Conditions/Comments
POWER SUPPLY
Supply Voltage, VDD
Average Operating Supply Current, ICC
3.0
3.30
170
5.5
2.55
5.5
215
10
2.8
2.4
V
µA
µA
V
V
0.0625 Conversions/Sec Rate1
Standby Mode
VDD Input, Disables ADC, Rising Edge
±1
1
±3
Undervoltage Lockout Threshold
Power-On Reset Threshold
2.35
1
TEMPERATURE-TO-DIGITAL CONVERTER
Local Sensor Accuracy
Resolution
Remote Diode Sensor Accuracy
35.7
142.8
°C
°C
°C
°C
°C
µA
µA
ms
5.7
22.8
ms
0.4
1
V
µA
IOUT = –6.0 mA2
VOUT = VDD2
V
VDD = 3 V to 5.5 V
V
mV
VDD = 3 V to 5.5 V
SDATA Forced to 0.6 V
ALERT Forced to 0.4 V
4.7
4
4.7
4
mA
mA
µA
pF
kHz
ms
µs
µs
µs
µs
SMBus Stop Condition Setup Time, tSU:STO
4
µs
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
SCLK, SDATA Rise Time, tR
SCLK, SDATA Fall Time, tF
250
ns
300
4.7
1
µs
µs
µs
1
300
µs
ns
±1
±3
Resolution
Remote Sensor Source Current
Conversion Time
0.125
230
13
OPEN-DRAIN DIGITAL OUTPUTS
(THERM, ALERT)
Output Low Voltage, VOL
High Level Output Leakage Current, IOH
SMBus INTERFACE2
Logic Input High Voltage, VIH
SCLK, SDATA
Logic Input Low Voltage, VIL
Hysteresis
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 Timeout
SMBus Clock Low Time, tLOW
SMBus Clock High Time, tHIGH
SMBus Start Condition Setup Time, tSU:STA
SMBus Start Condition Hold Time, tHD:STA
0.1
2.1
0.8
500
6
1
–1
+1
5
25
100
64
0 ≤ TA ≤ 100°C, VCC = 3 V to 3.6 V
60°C ≤ TD ≤ 100°C, VCC = 3 V to 3.6 V
0°C ≤ TD ≤ 120°C
High Level, Note 2
Low Level, Note 2
From Stop Bit to Conversion Complete
(Both Channels) One-Shot Mode with
Averaging Switched On
One-Shot Mode with Averaging Off
(i.e., Conversion Rate = 32 or 64
Conversions per Second)
Note 3
tLOW between 10% Points
tHIGH between 90% Points
Time from 10% of SDATA to 90%
of SCLK
Time from 90% of SCLK to 10%
of SDATA
Time for 10% or 90% of SDATA to
10% of SCLK
Between Start/Stop Condition
Master Clocking in Data
NOTES
1
See Table VI for information on other conversion rates.
2
Guaranteed by Design, not production tested.
3
The SMBus timeout is a programmable feature. By default it is not enabled. Details on how to enable it are available in the SMBus section of this data sheet.
Specifications subject to change without notice.
–2–
REV. 0
ADM1032
ABSOLUTE MAXIMUM RATINGS*
THERMAL CHARACTERISTICS
Positive Supply Voltage (VDD) to GND . . . . . . –0.3 V, +5.5 V
D+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to VDD + 0.3 V
D– to GND . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +0.6 V
SCLK, SDATA, ALERT . . . . . . . . . . . . . . . . –0.3 V to +5.5 V
THERM . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to VDD + 0.3 V
Input Current, SDATA, THERM . . . . . . . . . . . –1, +50 mA
Input Current, D– . . . . . . . . . . . . . . . . . . . . . . . . . . . . ± 1 mA
ESD Rating, All Pins (Human Body Model) . . . . . . >1000 V
Maximum Junction Temperature (TJ max) . . . . . . . . . 150°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
IR Reflow Peak Temp . . . . . . . . . . . . . . . . . . . . . . . . . 220°C
Lead Temp (Soldering 10 sec) . . . . . . . . . . . . . . . . . . . 300°C
8-Lead SO Package
θJA = 121°C/W
8-Lead Micro_SO Package
θJA = 142°C/W
PIN CONFIGURATION
VDD 1
8
SCLK
D+ 2
7
SDATA
ADM1032
TOP VIEW 6 ALERT
(Not to Scale)
5 GND
THERM 4
D– 3
*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.
ORDERING GUIDE
Model
Temperature
Range
Package
Description
Package
Option
Branding
Information
SMBus
Addr
ADM1032AR
ADM1032ARM
0°C to 120°C
0°C to 120°C
8-Lead SO Package
8-Lead Micro_SO Package
SO-8
RM-8
1032AR
T2A
4C
4C
tLOW
tR
tF
tHD;STA
SCLK
tHD;STA
tHD;DAT
tHIGH
tSU;STA
tSU;DAT
tSU;STO
SDATA
tBUF
P
S
S
P
Figure 1. Diagram for Serial Bus Timing
PIN FUNCTION DESCRIPTIONS
Pin
No.
Mnemonic
Description
1
2
3
4
VDD
D+
D–
THERM
5
6
7
8
GND
ALERT
SDATA
SCLK
Positive Supply, 3 V to 5.5 V.
Positive Connection to Remote Temperature Sensor.
Negative Connection to Remote Temperature Sensor.
Open-drain output that can be used to turn a fan on/off or throttle a CPU clock in the event of an overtemperature condition. Requires pull-up to VDD.
Supply Ground Connection
Open-Drain Logic Output Used as Interrupt or SMBus Alert.
Logic Input/Output, SMBus Serial Data. Open-Drain Output. Requires pull-up resistor.
Logic Input, SMBus Serial Clock. Requires pull-up resistor.
REV. 0
–3–
ADM1032–Typical Performance Characteristics
20
1.0
13
12
8
4
D+ TO GND
0
–4
D+ TO V DD
–8
TEMPERATURE ERROR – C
TEMPERATURE ERROR – C
TEMPERATURE ERROR – C
16
0.5
0
11
9
7
5
VIN = 40mV p-p
3
1
–12
VIN = 10mV p-p
–0.5
–16
0
10
LEAKAGE RESISTANCE – M
100
TPC 1. Temperature Error vs.
Leakage Resistance
0
20
40
60
80
TEMPERATURE – C
100
120
TPC 2. Temperature Error vs. Actual
Temperature Using 2N3906
12
–1
100k
10M
1M
FREQUENCY – Hz
100M
TPC 3. Temperature Error vs.
Differential Mode Noise Frequency
2.0
18
VIN = 250mV p-p
8
6
4
VIN = 100mV p-p
14
SUPPLY CURRENT – A
TEMPERATURE ERROR – C
TEMPERATURE ERROR – C
16
10
12
10
8
6
4
1.5
1.0
VDD = 5V
0.5
2
2
VDD = 3V
10
1M
1
6
FREQUENCY – Hz
TPC 4. Temperature Error vs. Power
Supply Noise Frequency
11
16
21
26
CAPACITANCE – nF
31
36
TPC 5. Temperature Error vs.
Capacitance between D+ and D–
12
VIN = 100mV p-p
8
6
4
VIN = 50mV p-p
60
50
VDD = 5V
40
30
20
2
10
VIN = 25mV p-p
0
100k
1M
10M
FREQUENCY – Hz
100M
TPC 7. Temperature Error vs.
Common-Mode Noise Frequency
100
40
70
10
0.1
1
10
CONVERSION RATE – Hz
TPC 6. Operating Supply Current vs.
Conversion Rate
80
SUPPLY CURRENT – A
TEMPERATURE ERROR – C
0
0.01
STANDBY SUPPLY CURRENT – A
0
0
35
30
25
20
15
10
5
VDD = 3.3V
0
0
1
5
10 25 50 75 100 250 500 750 1000
SCLK FREQUENCY – kHz
TPC 8. Standby Supply Current vs.
Clock Frequency
–4–
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
SUPPLY VOLTAGE – V
TPC 9. Standby Supply Current vs.
Supply Voltage
REV. 0
ADM1032
FUNCTIONAL DESCRIPTION
Figure 2 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.
The ADM1032 is a local and remote temperature sensor and
over-temperature alarm. When the ADM1032 is operating
normally, the on-board 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.
The measurement results are compared with local and remote,
high, low and THERM temperature limits, stored in nine onchip 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. Exceeding THERM
temperature limits cause the THERM output to assert low.
To measure ∆VBE, the sensor is switched between operating currents of I and N × 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 two’s complement format. To further
reduce the effects of noise, digital filtering is performed by averaging the results of 16 measurement cycles.
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.
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.
Signal conditioning and measurement of the internal temperature sensor is performed in a similar manner.
TEMPERATURE DATA FORMAT
One LSB of the ADC corresponds to 0.125°C, so the ADC can
measure from 0°C to 127.875°C. The temperature data format
is shown in Tables I and II.
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 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 technique used in the ADM1032 is to measure the change
in VBE when the device is operated at two different currents.
Table I. Temperature Data Format (Local Temperature and
Remote Temperature High Byte)
This is given by:
∆VBE = (n f ) KT × In ( N )
q
where:
K is Boltzmann’s constant (1.38 × 10–23).
q is charge on the electron (1.6 × 10–19 Coulombs).
T is absolute temperature in Kelvins.
N is ratio of the two currents.
nf is the ideality factor of the thermal diode.
The ADM1032 is trimmed for an ideality factor of 1.008.
Temperature
Digital Output
0°C
1°C
10°C
25°C
50°C
75°C
100°C
125°C
127°C
0
0
0
0
0
0
0
0
0
000
000
000
001
011
100
110
111
111
VDD
I
NI
IBIAS
D+
REMOTE
SENSING
TRANSISTOR
VOUT+
TO ADC
C1*
D–
BIAS
DIODE
LOW-PASS FILTER
fC = 65kHz
*CAPACITOR C1 IS OPTIONAL. IT SHOULD ONLY BE USED IN NOISY ENVIRONMENTS.
C1 = 2.2nF TYPICAL, 3nF MAX.
Figure 2. Input Signal Conditioning
REV. 0
–5–
VOUT–
0000
0001
1010
1001
0010
1011
0100
1101
1111
ADM1032
Table II. Extended Temperature Resolution (Remote
Temperature Low Byte)
Extended
Resolution
Remote Temperature
Low Byte
0.000°C
0.125°C
0.250°C
0.375°C
0.500°C
0.625°C
0.750°C
0.875°C
0
0
0
0
1
1
1
1
000
010
100
110
000
010
100
110
Status Register
Bit 7 of the Status Register indicates that the ADC is busy converting 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.
0000
0000
0000
0000
0000
0000
0000
0000
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 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.
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.
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.
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.
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.
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.
Table IV. Status Register Bit Assignments
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 temperature 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.
12h
–4°C
–1°C
–0.125°C
0°C
+0.125°C
+1°C
+4°C
1
1
1
0
0
0
0
0
0
1
0
0
0
0
111 1100
111 1111
111 1111
000 0000
000 0000
000 0001
000 0100
000
000
110
000
010
000
000
Function
7
6
5
4
3
2
1
0
BUSY
LHIGH*
LLOW*
RHIGH*
RLOW*
OPEN*
RTHRM
LTHRM
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
1 When Remote Therm Limit Tripped
1 When Local Therm Limit Tripped
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.
Table III. Sample Offset Register Codes
11h
Name
*These flags stay high until the status register is read or they are reset by POR.
The offset register powers up with a default value of 0°C, and
will have no effect if nothing is written to them.
Offset Value
Bit
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.
0000
0000
0000
0000
0000
0000
0000
–6–
REV. 0
ADM1032
Table V. Configuration Register Bit Assignments
Power-On
Default
Bit
Name
Function
7
MASK1
6
RUN/STOP
0 = ALERT Enabled
1 = ALERT Masked
0 = Run
1 = Standby
Reserved
5–0
0
0
Consecutive ALERT Register
This value written to this register determines how many out-oflimit measurements must occur before an ALERT is generated.
The default value is that one out-of-limit measurement generates an ALERT. The max value that can be chosen is 4. The
purpose of this register is to allow the user to perform some filtering of the output. This is particularly useful at the faster two
conversion rates where no averaging takes place.
0
Table VII.
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.
Conversion/sec
00h
01h
02h
03h
04h
05h
06h
07h
08h
09h
0Ah
0B to FFh
0.0625
0.125
0.25
0.5
1
2
4
8
16
32
64
Reserved
Average Supply Current
mA Typ at VDD = 5.5 V
0.17
0.20
0.21
0.24
0.29
0.40
0.61
1.1
1.9
0.73
1.23
Limit Registers
Number of “Out-of-Limit”
Measurements Required
yxxx 000x
yxxx 001x
yxxx 011x
yxxx 111x
1
2
3
4
NOTES
x = Don’t care bit.
y = SMBus timeout bit. Default = 0. See SMBus section for more
information.
Table VI. Conversion Rate Register Codes
Data
Register Value
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. However, 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) = x8 + x2 + x1 + 1
Consult SMBus 1.1 specification for more information
(www.smbus.org).
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.
ADDRESSING THE DEVICE
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 81oC
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).
The serial bus protocol operates as follows:
One-Shot Register
The One-Shot Register is used to initiate a single conversion
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 irrelevant 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
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 available with one device address, which is Hex 4C (1001 100).
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
–7–
ADM1032
Table VIII. List of ADM1032 Registers
Read Address (Hex)
Write Address (Hex)
Name
Power-On Default
Not Applicable
00
01
02
03
04
05
06
07
08
Not Applicable
10
11
12
13
14
19
20
21
22
FE
FF
Not Applicable
Not Applicable
Not Applicable
Not Applicable
09
0A
0B
0C
0D
0E
0F
Not Applicable
11
12
13
14
19
20
21
22
Not Applicable
Not Applicable
Address Pointer
Local Temperature Value
External Temperature Value High Byte
Status
Configuration
Conversion Rate
Local Temperature High Limit
Local Temperature Low Limit
External Temperature High Limit High Byte
External Temperature Low Limit High Byte
One-Shot
External Temperature Value Low Byte
External Temperature Offset High Byte
External Temperature Offset Low Byte
External Temperature High Limit Low Byte
External Temperature Low Limit Low Byte
External THERM Limit
Local THERM Limit
THERM Hysteresis
Consecutive ALERT
Manufacturer ID
Die Revision Code
Undefined
0000 0000 (00h)
0000 0000 (00h)
Undefined
0000 0000 (00h)
0000 1000 (08h)
0101 0101 (55h) (85°C)
0000 0000 (00h) (0°C)
0101 0101 (55h) (85°C)
0000 0000 (00h) (0°C)
0000 0000
0000 0000
0000 0000
0000 0000
0000 0000
0101 0101 (55h) (85°C)
0101 0101 (55h) (85°C)
0000 1010 (0Ah) (10°C)
0000 0001 (01h)
0100 0001 (41h)
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 matter what data is written to it.
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.
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.
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.
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 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.
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.
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.
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.
In the case of the ADM1032, write operations contain either one
or two bytes, while read operations contain one byte, and perform the following functions:
–8–
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.
REV. 0
ADM1032
2. Don’t forget that some of the ADM1032 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. 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.
1
9
1
9
SCLK
A6
SDATA
A5
A4
A3
A2
A1
A0
R/W
START BY
MASTER
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1032
ACK. BY
ADM1032
FRAME 2
ADDRESS POINTER REGISTER BYTE
FRAME 1
SERIAL BUS ADDRESS BYTE
1
9
SCLK (CONTINUED)
D7
SDATA (CONTINUED)
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1032
STOP BY
MASTER
FRAME 3
DATA BYTE
Figure 3a. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
1
9
1
9
SCLK
SDATA
START BY
MASTER
A6
A5
A4
A3
A2
A1
A0
R/W
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1032
ACK. BY
ADM1032
FRAME 1
SERIAL BUS ADDRESS BYTE
STOP BY
MASTER
FRAME 2
ADDRESS POINTER REGISTER BYTE
Figure 3b. Writing to the Address Pointer Register Only
1
9
1
9
SCLK
SDATA
A6
A5
A4
A3
A2
A1
A0
R/W
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1032
START BY
MASTER
ACK. BY
ADM1032
FRAME 1
SERIAL BUS ADDRESS BYTE
STOP BY
MASTER
FRAME 2
DATA BYTE FROM ADM1032
Figure 3c. Reading Data from a Previously Selected Register
ALERT OUTPUT
The ALERT output goes low whenever an out-of-limit measurement is detected, or if the remote temperature sensor is
open-circuit. It is an open drain and requires a pull-up to VDD.
Several ALERT outputs can be wire-ORed together, so that the
common line will go low if one or more of the ALERT outputs
goes low.
One or more ALERT outputs can be 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 4.
MASTER
RECEIVES
SMBALERT
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.
REV. 0
START
ALERT RESPONSE ADDRESS
MASTER SENDS
ARA AND READ
COMMAND
RD
ACK
DEVICE ADDRESS
DEVICE SENDS
ITS ADDRESS
Figure 4. Use of SMBALERT
–9–
NO
ACK
STOP
ADM1032
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.
As the device address is seven bits, an LSB of ‘1’ is added.
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.
A THERM Hysteresis Value is provided to prevent a cooling fan
cycling on and off. The power-on default value is 10°C but this
may be reprogrammed to any value after power-up. This hysteresis value applies to both the local and remote channels
Using these two limits in this way allows the user to gain maximum performance from the system by only slowing it down,
should it be at a critical temperature.
The THERM signal is open drain and requires a pull-up to
VDD. The THERM signal must always be pulled up to the same
power supply as the ADM1032, unlike the SMBus signals
(SDATA, SCLK, and ALERT) which may be pulled to a different power rail, usually that of the SMBus controller.
5. Once the ADM1032 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.
100C
90C
70C
60C
LOW-POWER STANDBY MODE
50C
The ADM1032 can be put into a low-power standby mode by setting
bit 6 of the Configuration Register. When Bit 6 is low, the ADM1032
operates normally. When Bit 6 is high, the ADC is inhibited, and
any conversion in progress is terminated without writing the result
to the corresponding value register.
40C
The SMBus is still enabled. Power consumption in the standby mode
is reduced to less than 10 µA if there is no SMBus activity, or 100 µA
if there are clock and data signals on the bus.
When the device is in standby mode, it is still possible to initiate a
one-shot conversion of both channels by writing XXh to the
One-Shot Register (address 0Fh), after which the device will return
to standby. It is also possible to write new values to the limit register while it is in standby. If the values stored in the temperature
value registers are now outside the new limits, an ALERT is
generated even though the ADM1032 is still in standby.
THE ADM1032 INTERRUPT SYSTEM
The ADM1032 has two interrupt outputs, ALERT and THERM.
These have different functions. ALERT responds to violations of
software-programmed temperature limits and is maskable. THERM
is intended as a “fail-safe” interrupt output that cannot be masked.
If the temperature goes equal to or below the lower temperature limit,
the ALERT pin will be asserted low to indicate an out-of-limit
condition. If the temperature is within the programmed low and
high temperature limits, no interrupt will be generated.
If the temperature exceeds the high temperature limit, the ALERT pin
will be asserted low to indicate an over temperature condition. A local
and remote THERM limit, may be programmed into the device to set
the temperature limit above which the over temperature THERM
pin will be asserted low. This temperature limit should be equal to
or greater than the high temperature limit programmed.
The behavior of the high limit and THERM limit is as follows:
1. If either temperature measured exceeds the high temperature
limit, the ALERT output will assert low.
2. If the local or remote temperature continues to increase and
either one exceeds the THERM limit, the THERM output
asserts low. This can be used to throttle the CPU clock or
switch on a fan.
LOCAL THERM
LIMIT
80C
TEMPERATURE
LOCAL THERM LIMIT
–HYSTERESIS
THERM
Figure 5. Operation of the THERM Output
Table IX. THERM HYSTERESIS Sample Values
THERM HYSTERESIS
Binary Representation
0°C
1°C
10°C
0 000 0000
0 000 0001
0 000 1010
SENSOR FAULT DETECTION
At the D+ input the ADM1032 has a fault detector that detects
if the external sensor diode is open-circuit. This is a simple
voltage comparator that trips if the voltage at D+ exceeds VDD –
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 0°C, 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 (0°C) and any low limit
that would normally be programmed, a short-circuit sensor will
cause an SMBus alert.
In this respect the ADM1032 differs from and improves upon,
competitive devices that output zero if the external sensor goes
short-circuit. These devices can misinterpret a genuine 0°C
measurement as a fault condition.
When the D+ and D– lines are shorted together, an ALERT
will always be generated. This is because the remote value register reports a temperature value of –128°C. Since the ADM1032
performs a less-than or equal-to comparison with the low limit,
an ALERT is generated even when the low limit is set to its
minimum of –128°C.
–10–
REV. 0
ADM1032
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.
APPLICATIONS INFORMATION
FACTORS AFFECTING ACCURACY
Remote Sensing Diode
The ADM1032 is designed to work with substrate transistors
built into processors’ CPUs 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 transistor connected as a diode (base shorted to collector).
If an NPN transistor is used, the collector and base are connected
to D+ and the emitter to D–. If a PNP transistor is used, the
collector and base are connected to D– and the emitter to D+.
Substrate transistors are found in a number of CPUs. To reduce
the error due to variations in these substrate and discrete
transistors, a number of factors should be taken into consideration:
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.
1. The ideality factor, nf, of the transistor. The ideality factor is
a measure of the deviation of the thermal diode from ideal
behavior. The ADM1032 is trimmed for an nf value of 1.008.
The following equation may be used to calculate the error
introduced at a temperature T°C when using a transistor
whose nf does not equal 1.008. Consult the processor
datasheet for nf values.
∆T =
(n
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 negligible. 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.
)
– 1.008
× (273.15 Kelvin + T )
1.008
natural
This value can be written to the offset register and is automatically added to or subtracted from the temperature measurement.
2. Some CPU manufacturers specify the high and low current
levels of the substrate transistors. The high current level of
the ADM1032, IHIGH, is 230 A and the low level current,
ILOW, is 13 A. If the ADM1032 current levels do not match
the levels of the CPU manufacturers, then it may become
necessary to remove an offset. The CPU’s datasheet will
advise whether this offset needs to be removed and how to
calculate it. This offset may be programmed to the offset
register. It is important to note that if accounting for two or
more offsets is needed, then the algebraic sum of these offsets
must be programmed to the Offset Register.
If a discrete transistor is being used with the ADM1032 the best
accuracy will be obtained by choosing devices according to the
following criteria:
• 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.
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:
1. Place the ADM1032 as close as possible to the remote sensing
diode. Provided that the worst noise sources, i.e., 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.
• Base resistance less than 100 Ω.
• Small variation in hFE (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.
GND
10MIL
D+
THERMAL INERTIA AND SELF-HEATING
REV. 0
10MIL
10MIL
D–
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
10MIL
10MIL
10MIL
GND
10MIL
Figure 6. 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.
–11–
ADM1032
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.
Thermocouple effects should not be a major problem as 1°C
corresponds to about 200 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 200 V.
APPLICATION CIRCUIT
Figure 7 shows a typical application circuit for the ADM1032,
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.
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 ADM1032. Leave the remote end of the shield unconnected
to avoid ground loops.
C01906–.8–10/01(0)
Cable resistance can also introduce errors. 1 Ω series resistance
introduces about 1°C error.
5. Place a 0.1 µF bypass capacitor close to the VDD pin. In very
noisy environments place a 2200 pF input filter capacitors
across D+, D– close to the ADM1032.
The SCLK, and SDATA pins of the ADM1032 can be interfaced directly to the SMBus of an I/O controller such as the
Intel 820 chipset.
0.1F
VDD
3V TO 3.6V
ADM1032
TYP 10k
D+
SCLK
D–
SHIELD
2N3906
OR
CPU THERMAL
DIODE
SMBUS
CONTROLLER
SDATA
5V OR 12V
ALERT
THERM
GND
VDD
TYP 10k
FAN CONTROL
CIRCUIT
FAN ENABLE
Figure 7. Typical Application Circuit
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead SO
(R-8)
8-Lead Micro_SO
(RM-8)
0.1574 (4.00)
0.1497 (3.80)
8
5
1
4
8
0.2440 (6.20)
0.2284 (5.80)
PRINTED IN U.S.A.
0.122 (3.10)
0.114 (2.90)
0.1968 (5.00)
0.1890 (4.80)
5
0.199 (5.05)
0.187 (4.75)
0.122 (3.10)
0.114 (2.90)
1
4
PIN 1
0.0196 (0.50)
45
0.0099 (0.25)
0.0500 (1.27)
BSC
0.0098 (0.25)
0.0040 (0.10)
SEATING
PLANE
PIN 1
0.0256 (0.65) BSC
0.0688 (1.75)
0.0532 (1.35)
0.0192 (0.49)
0.0138 (0.35)
0.120 (3.05)
0.112 (2.84)
8
0.0500 (1.27)
0.0098 (0.25) 0
0.0160 (0.41)
0.0075 (0.19)
0.006 (0.15)
0.002 (0.05)
0.015 (0.38)
SEATING 0.009 (0.22)
PLANE
–12–
0.120 (3.05)
0.112 (2.84)
0.043 (1.09)
0.037 (0.94)
0.009 (0.23)
0.003 (0.08)
6
0
0.028 (0.71)
0.016 (0.41)
REV. 0
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