ADM1034 datasheet(17/40 Pages) AD

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ADM1034

Rev. 0 | Page 17 of 40

The ADM1034 operates at three different currents to measure

the change in Vbe. Figure 28 shows the input signal conditioning

used to measure the output of an external temperature sensor. It

also shows the external sensor as a substrate transistor, provided

for temperature monitoring on some microprocessors. The

external sensor could work equally well as a discrete transistor.

If a discrete transistor is used, the collector is not grounded, and

should be 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.

If the sensor is used in a very noisy environment, a capacitor

value up to 1000 pF may be placed between the D+ and D−

inputs to filter the noise. However, additional parasitic

capacitance on the lines between D+, D−, and the thermal diode

should also be considered. The total capacitance should never

be greater than 1000 pF.

To measure each ∆Vbe, the sensor is switched between operating

currents of I, (N1 × I), and (N2 × I). The resulting waveform is

passed through a 65 kHz low-pass filter to remove noise, then to

a chopper-stabilized amplifier that amplifies and rectifies the

waveform. This produces a dc voltage proportional to ∆Vbe.

These voltage measurements determine the temperature of the

thermal diode, while automatically compensating for any series

resistance on the D+ and/or D− lines. The temperature is stored

in two registers as a 13-bit word.

To further reduce the effects of noise, digital filtering is

performed by averaging the results of 16 measurement cycles at

conversion rates of less than or equal to 8 Hz. An external

temperature measurement takes nominally 32 ms when

averaging is enabled and 6 ms when averaging is disabled.

One LSB of the ADC corresponds to 0.03125°C. The ADM1034

can theoretically measure temperatures from −64°C to

+191.96875°C, although these are outside its operating range.

The extended temperature resolution data format is shown in

Table 8. The data for the local and remote channels is stored in

the extended temperature resolution registers (Reg. 0x40 =

Local, Reg. 0x42 = Remote 1, and Reg. 0x44 = Remote 2).

Table 9.Temperature Measurement Registers

Description

Default

0x40

Local Temperature, LSBs

0x00

0x41

Local Temperature, MSBs

0x00

0x42

Remote 1 Temperature, LSBs

0x00

0x43

Remote 1 Temperature, MSBs

0x00

0x44

Remote 2 Temperature, LSBs

0x00

0x45

Remote 2 Temperature, MSBs

0x00

High and low temperature limit registers are associated with

each temperature measurement channel. Exceeding the

programmed high and low limits sets the appropriate status bit.

Exceeding either limit can cause an SMBusALERT interrupt.

Table 10. Temperature Measurement Limit Registers

Description

Default

0x0B

Local High Limit

0x8B (75°C)

0x0C

Local Low Limit

0x54 (20°C)

0x0D

Local THERM Limit

0x95 (85°C)

0x0E

Remote 1 High Limit

0x8B (75°C)

0x0F

Remote 1 Low Limit

0x54 (20°C)

0x10

Remote 1 THERM Limit

0x95 (85°C)

0x11

Remote 2 High Limit

0x8B (75°C)

0x12

Remote 2 Low Limit

0x54 (20°C)

0x13

Remote 2 THERM Limit

0x95 (85°C)

D+

D–

REMOTE

SENSING

TRANSISTOR

IN1

× I

IBIAS

VDD

VOUT+

TO ADC

VOUT–

LOW-PASS FILTER

fC = 65kHz

Figure 28. ADM1034 Signal Conditioning

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