ADM1032

http://onsemi.com

7

Functional Description

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

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 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:

Standby Mode

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

from device to device.

The technique used in the ADM1032 is to measure the

currents.

This is given by:

(eq. 1)

KT

q

In(N)

where:

T is the absolute temperature in Kelvins

N is the ratio of the two currents

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,

provided

for

temperature

monitoring

on

some

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.

To measure

operating currents of I and N  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

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

measurement cycles.

Signal conditioning and measurement of the internal

temperature sensor is performed in a similar manner.

Figure 12. Input Signal Conditioning

LOW-PASS FILTER

REMOTE

SENSING

TRANSISTOR

BIAS

DIODE

D+

D−

IN  I

To ADC

C1*

* CAPACITOR C1 IS OPTIONAL AND IT SHOULD ONLY BE USED IN VERY NOISY ENVIRONMENTS. C1 = 1000 pF Max.