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ADM1032 Datasheet(PDF) 7 Page - ON Semiconductor
ONSEMI [ON Semiconductor]
ADM1032 Datasheet(HTML) 7 Page - ON Semiconductor
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The ADM1032 is a local and remote temperature sensor
and overtemperature alarm. When the ADM1032 is
operating normally, the on−board A/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 are stored in the local and remote temperature value
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 cause the ALERT output to pull low.
Exceeding THERM temperature limits causes the THERM
output to assert low.
The limit registers can be programmed, and the device
controlled and configured, via the serial 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
Masking or enabling the ALERT output.
Selecting the conversion rate.
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 V
, which varies
from device to device.
The technique used in the ADM1032 is to measure the
change in V
when the device is operated at two different
This is given by:
K is Boltzmann’s constant (1.38 x 10
q is the charge on the electron (1.6 x 10
T is the absolute temperature in Kelvins.
N is the ratio of the two currents.
is the ideality factor of the thermal diode.
The ADM1032 is trimmed for an ideality factor of 1.008.
Figure 12 shows the input signal conditioning used to
measure the output of an external temperature sensor.
Figure 12 shows the external sensor as a substrate transistor,
microprocessors, but it could equally well be a discrete
transistor. If a discrete transistor is used, the collector is not
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
can optionally be added as a noise filter. Its value should be
no more than 1000 pF. See the Layout Considerations
section for more information on C1.
, the sensor is switched between the
operating currents of I and N x I. The resulting waveform is
passed through a 65 kHz low−pass filter to remove noise,
and then to a chopper−stabilized amplifier that performs the
functions of amplification and rectification of the waveform
to produce a dc voltage proportional to
. This voltage
is measured by the ADC to give a temperature output in twos
complement format. To further reduce the effects of noise,
digital filtering is performed by averaging the results of 16
Signal conditioning and measurement of the internal
temperature sensor is performed in a similar manner.
Figure 12. Input Signal Conditioning
CAPACITOR C1 IS OPTIONAL AND IT SHOULD ONLY BE USED IN VERY NOISY ENVIRONMENTS. C1 = 1000pF MAX.
N × I
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