ADM1031ARQZ 查看數據表（PDF） - ON Semiconductor

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ADM1031ARQZ

Intelligent Temperature Monitor and Dual PWM Fan Controller

ON Semiconductor 

ADM1031

I

N × I IBIAS

VDD

D+

REMOTE

SENSING

TRANSISTOR D–

BIAS

DIODE

LOW−PASS

FILTER

fC = 65kHz

VOUT+

TO

ADC

VOUT–

Figure 18. Signal Conditioning

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)

−128°C

−125°C

−100°C

−75°C

−50°C

−25°C

−1°C

0°C

+1°C

+10°C

+25°C

+50°C

+75°C

+100°C

+125°C

+127°C

Digital Output

1000 0000

1000 0011

1001 1100

1011 0101

1100 1110

1110 0111

1111 1111

0000 0000

0000 0001

0000 1010

0001 1001

0011 0010

0100 1011

0110 0100

0111 1101

0111 1111

Table 3. Remote Sensor Extended Temperature

Resolution

Extended Resolution

0.000°C

0.125°C

Remote Temperature Low Bits

000

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

0.00°C

0.25°C

0.50°C

0.75°C

Local Temperature Low Bits

00

01

10

11

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.

GND

D+

D–

GND

10MIL

10MIL

10MIL

10MIL

10MIL

10MIL

10MIL

Figure 19. Arrangement of Signal Tracks

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