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PDF ADM1032 Data sheet ( Hoja de datos )
| Número de pieza | ADM1032 | |
| Descripción | +-1C Remote and Local System Temperature Monitor | |
| Fabricantes | Analog Devices | |
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a
؎1؇C Remote and Local
System Temperature Monitor
ADM1032*
FEATURES
On-Chip and Remote Temperature Sensing
Offset Registers for System Calibration
0.125؇C Resolution/1؇C Accuracy on Remote Channel
1؇C Resolution/3؇C 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
APPLICATIONS
Desktop Computers
Notebook Computers
Smart Batteries
Industrial Controllers
PRODUCT DESCRIPTION
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 mea-
sures 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.
Telecomms Equipment
Instrumentation
Embedded Systems
FUNCTIONAL BLOCK DIAGRAM
ON-CHIP
TEMPERATURE
SENSOR
LOCAL TEMPERATURE
VALUE REGISTER
D+ ANALOG
A-TO-D
D–
MUX
CONVERTER
BUSY
RUN/STANDBY
REMOTE TEMPERATURE
VALUE REGISTER
REMOTE OFFSET
REGISTER
EXTERNAL DIODE OPEN-CIRCUIT
ADM1032
LIMIT
COMPARATOR
STATUS REGISTER
ADDRESS POINTER
REGISTER
CONVERSION RATE
REGISTER
LOCAL TEMPERATURE
LOW-LIMIT REGISTER
LOCAL TEMPERATURE
HIGH-LIMIT REGISTER
REMOTE TEMPERATURE
LOW-LIMIT REGISTER
REMOTE TEMPERATURE
HIGH-LIMIT REGISTER
LOCAL THERM LIMIT
REGISTER
EXTERNAL THERM LIMIT
REGISTER
CONFIGURATION
REGISTER
INTERRUPT
MASKING
SMBUS INTERFACE
ALERT
THERM
VDD GND
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.
SDATA
SCLK
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
1 page  
ADM1032
FUNCTIONAL DESCRIPTION
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 free-
running mode. The analog input multiplexer alternately selects
either the on-chip temperature sensor to measure its local tem-
perature, 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 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. Exceeding THERM
temperature limits cause the THERM output to assert low.
The limit registers can be programmed, and the device con-
trolled 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.
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. Unfortu-
nately, 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 ADM1032 is to measure the change
in VBE when the device is operated at two different currents.
This is given by:
where:
∆VBE
= (nf )
KT
q
×
In (N )
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.
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 tem-
perature 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 measure-
ment, 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 typi-
cally 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 cur-
rents of I and N × I. The resulting waveform is passed through
a 65 kHz low-pass filter to remove noise, thence to a chopper-
stabilized amplifier that performs the functions of amplification
and rectification of the waveform to produce a dc voltage pro-
portional 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 aver-
aging the results of 16 measurement cycles.
Signal conditioning and measurement of the internal tempera-
ture 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.
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.
Table I. Temperature Data Format (Local Temperature and
Remote Temperature High Byte)
Temperature
0°C
1°C
10°C
25°C
50°C
75°C
100°C
125°C
127°C
Digital Output
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
REV. 0
VDD
I
N؋I
IBIAS
REMOTE
SENSING
TRANSISTOR
D+
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
–5–
VOUT+
TO ADC
VOUT–
5 Page 
ADM1032
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. Sub-
strate 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:
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 = nnatural – 1.008 × 273.15 Kelvin + T
1.008
This value can be written to the offset register and is automati-
cally 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.
temperature change. In the case of the remote sensor this should
not be a problem, as it will either be a substrate transistor in the
processor, or can be a small package device such as SOT-23
placed in close proximity to it.
The on-chip sensor, however, will often be remote from the
processor, and will only be monitoring the general ambient
temperature around the package. The thermal time constant of
the SO-8 package in still air is about 140 seconds, and if the ambient
air temperature quickly changed by 100 degrees, it would take about
12 minutes (5 time constants) for the junction temperature of the
ADM1032 to settle within 1 degree of this. In practice, the ADM1032
package will be in electrical, and hence thermal, contact with a printed
circuit board, and may also be in a forced airflow. How accurately
the temperature of the board and/or the forced airflow reflect the
temperature to be measured will also affect the accuracy.
Self-heating due to the power dissipated in the ADM1032 or the
remote sensor, causes the chip temperature of the device or remote
sensor to rise above ambient. However, the current forced through
the remote sensor is so small that self-heating is 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.
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 gen-
erators, data/address buses, and CRTs, are avoided, this distance
can be 4 to 8 inches.
2. Route the D+ and D– tracks close together, in parallel, with
grounded guard tracks on each side. Provide a ground plane
under the tracks if possible.
3. Use wide tracks to minimize inductance and reduce noise
pickup. 10 mil track minimum width and spacing is
recommended.
• 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
D+
10MIL
10MIL
10MIL
10MIL
THERMAL INERTIA AND SELF-HEATING
Accuracy depends on the temperature of the remote-sensing
diode and/or the internal temperature sensor being at the same
temperature as that being measured, and a number of factors
can affect this. Ideally, the sensor should be in good thermal
contact with the part of the system being measured, for example
the processor. If it is not, the thermal inertia caused by the mass
of the sensor will cause a lag in the response of the sensor to a
D–
GND
10MIL
10MIL
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.
REV. 0
–11–
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet ADM1032.PDF ] | |
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