ADM1031ARQZ-R7 datasheet(10/30 Pages) ONSEMI

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ADM1031

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Figure 18. Signal Conditioning

REMOTE

SENSING

TRANSISTOR

BIAS

DIODE

D+

D–

ADC

LOW−PASS

FILTER

fC = 65kHz

VDD

VOUT+

VOUT–

IBIAS

IN × I

If a discrete transistor is used, then the collector is not

grounded, and is linked to the base. If a PNP transistor is

used, the base is connected to the D– input and the emitter

to the D+ input. If an NPN transistor is used, the emitter is

connected to the D– input and the base to the D+ input.

One LSB of the ADC corresponds to 0.125

°C, so the

ADM1031 can theoretically measure temperatures from

–127

°C to +127.75°C, although –127°C is outside the

operating range for the device. The extended temperature

resolution data format is shown in Table 3 and Table 4.

Table 2. Temperature Data Format − (Local

Temperature and Remote Temperature High Bytes)

Temperature (5C)

Digital Output

−128°C

1000 0000

−125°C

1000 0011

−100°C

1001 1100

−75°C

1011 0101

−50°C

1100 1110

−25°C

1110 0111

−1°C

1111 1111

0°C

0000 0000

+1°C

0000 0001

+10°C

0000 1010

+25°C

0001 1001

+50°C

0011 0010

+75°C

0100 1011

+100°C

0110 0100

+125°C

0111 1101

+127°C

0111 1111

Table 3. Remote Sensor Extended Temperature

Resolution

Extended Resolution

Remote Temperature Low Bits

0.000°C

000

0.125°C

001

0.250°C

010

0.375°C

011

0.500°C

100

0.625°C

101

0.750°C

110

0.875°C

111

The extended temperature resolution for the local and

remote channels is stored in the extended temperature

resolution register (Register 0

×06), and is outlined in Table 27.

Table 4. Local Sensor Extended Temperature

Resolution

Extended Resolution

Local Temperature Low Bits

0.00°C

0.25°C

0.50°C

0.75°C

To prevent ground noise interfering with the

measurement, the more negative terminal of the sensor is not

referenced to ground, but biased above ground by an internal

diode at the D– input. If the sensor is used in a very noisy

environment, a capacitor of value up to 1000 pF can be

placed between the D+ and D– inputs to filter the noise.

To measure

DVBE, 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,

then to a chopper−stabilized amplifier that performs the

functions of amplification and rectification of the waveform

to produce a dc voltage proportional to

DVBE. This voltage

is measured by the ADC to give a temperature output in

11−bit twos complement format. To further reduce the

effects of noise, digital filtering is performed by averaging

the results of 16 measurement cycles. An external

temperature measurement nominally takes 9.6 ms.

Layout Considerations

Digital boards can be electrically noisy environments and

care must be taken to protect the analog inputs from noise,

particularly when measuring the very small voltages from a

remote diode sensor. The following precautions should be

taken:

1. Place the ADM1031 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. Ten mil track minimum

width and spacing is recommended.

Figure 19. Arrangement of Signal Tracks

10MIL

GND

D+

GND

D–

10MIL

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