ADT7467ARQZ-R7 datasheet(19/77 Pages) ONSEMI

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ADT7467

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2N3904

NPN

ADT7467

D+

D–

Figure 25. Measuring Temperature Using an NPN Transistor

2N3906

PNP

ADT7467

D+

D–

Figure 26. Measuring Temperature Using a PNP Transistor

Nulling Temperature Errors

As CPUs run faster, it is more difficult to avoid high frequency

clocks when routing the D+/D− traces around a system board.

Even when recommended layout guidelines are followed, some

temperature errors may still be attributed to noise coupled onto

the D+/D− lines. Constant high frequency noise usually attenuates

or increases temperature measurements by a linear, constant value.

The ADT7467 has temperature offset registers at Address 0x70

and Address 0x72 for the Remote 1 and Remote 2 temperature

channels, respectively. By performing a one-time calibration of

the system, the user can determine the offset caused by system

board noise and null it using the offset registers. The offset

registers automatically add an Offset 64/twos complement 8-bit

reading to every temperature measurement. The LSBs add

0.5°C offset to the temperature reading; therefore, the 8-bit

with a resolution of 0.5°C. This ensures that the readings in the

temperature measurement registers are as accurate as possible.

Temperature Offset Registers

ADT7460/ADT7467 Backwards-Compatible Mode

By setting Bit 1 of Configuration Register 5 (0x7C), all tempera-

ture measurements are stored in the zone temperature value

registers (Register 0x25, Register 0x26, and Register 0x27) in

twos complement format in the range −128°C to +127°C. (The

ADT7468 makes calculations based on the Offset 64 extended

range and clamps the results if necessary.) The temperature

limits must be reprogrammed in twos complement format. If a

twos complement temperature below −63°C is entered, the

temperature is clamped to −63°C. In this mode, the diode fault

condition remains −128°C = 1000 0000, whereas the fault

condition is represented by −64°C = 0000 0000 in the extended

temperature range (−64°C to +191°C).

Temperature Measurement Registers

<7:6> TDM2, Remote 2 temperature LSBs

<5:4> LTMP, local temperature LSBs

<3:2> TDM1, Remote 1 temperature LSBs

Temperature Measurement Limit Registers

High and low limit registers are associated with each tempera-

ture measurement channel. Exceeding the programmed high or

low limit sets the appropriate status bit and can also generate

SMBALERT interrupts.

Reading Temperature from the ADT7467

It is important to note that temperature can be read from the

ADT7467 as an 8-bit value (with 1°C resolution) or as a 10-bit

value (with 0.25°C resolution). If only 1°C resolution is required,

the temperature readings can be read at any time and in no

particular order.

If the 10-bit measurement is required, this involves a 2-register

read for each measurement. The extended resolution register

(0x77) should be read first. Then all temperature reading

registers freeze until all temperature reading registers are read.

This prevents updating of an MSB reading while its two LSBs

are read and vice versa.

ADDITIONAL ADC FUNCTIONS FOR

TEMPERATURE MEASUREMENT

A number of other functions are available on the ADT7467 to

offer the system designer increased flexibility.

Turn-Off Averaging

For each temperature measurement read from a value register,

16 readings are made internally, the results of which are averaged

and then placed into the value register. Sometimes it is necessary

to perform a very fast measurement. Setting Bit 4 of Configuration

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