ADM1029ARQ 查看數據表（PDF） - Analog Devices

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ADM1029ARQ

Dual PWM Fan Controller and Temperature Monitor for High Availability Systems

Analog Devices 

ADM1029

VDD

I

N ؋ I IBIAS

D+

REMOTE

SENSING

TRANSISTOR

D–

BIAS

DIODE

LOW-PASS FILTER

fC = 65kHz

VOUT+

TO ADC

VOUT–

Figure 5. Signal Conditioning for Remote Diode Temperature Sensors

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 noisy environment, a capacitor of value

up to 1000 pF may be placed between the D+/D– pins.

To measure ∆VBE, 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, and to a chopper-stabilized amplifier

that performs the functions of amplification and rectification of

the waveform to produce a dc voltage proportional to ∆VBE. This

voltage is measured by the ADC to give a temperature output in

8-bit two’s 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 takes

nominally 9.6 ms.

The results of external temperature measurements are stored in

8-bit, two’s complement format, as illustrated in Table II.

OFFSET REGISTERS

Digital noise and other error sources can cause offset errors in

the temperature measurement, particularly on the remote sen-

sors. The ADM1029 offers a way to minimize these effects. The

offsets on the three temperature channels can be measured during

system characterization and stored as two’s complement values

in three offset registers at addresses 30h to 32h. The offset

values are automatically added to, or subtracted from, the tem-

perature values, depending on whether the two’s complement

number corresponds to a positive or negative offset. Offset val-

ues from –15°C to +15°C are allowed.

The default value in the offset registers is zero, so if no offsets

are programmed, the temperature measurements are unaltered.

TEMPERATURE LIMITS

The contents of the Local and Remote Temperature Value Regis-

ters (addresses A0h to A2h) are compared to the contents of the

High and Low Limit Registers at addresses 90h to 92h and 98h

to 9Ah. How the ADM1029 responds to overtemperature/

undertemperature conditions depends on the status of the Tem-

perature Fault Action Registers (addresses 40h to 42h). The

response of CFAULT, INT, and fan-speed-to-temperature events

depends on the setting of these registers, as explained later.

Table II. Temperature Data Format

Temperature

–128°C

–125°C

–100°C

–75°C

–50°C

–25°C

0°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

0000 0000

0000 1010

0001 1001

0011 0010

0100 1011

0110 0100

0111 1101

0111 1111

–10–

REV. 0

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