ADT7467ARQZ-R7 datasheet(24/77 Pages) ONSEMI

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ADT7467

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THERM

TMIN

THERM ASSERTED TO LOW AS AN INPUT:

FANS DO NOT GO TO 100% BECAUSE

TEMPERATURE IS BELOW TMIN

THERM ASSERTED TO LOW AS AN INPUT:

FANS DO NOT GO TO 100% BECAUSE

TEMPERATURE IS ABOVE TMIN AND FANS

ARE ALREADY RUNNING

Figure 30. Asserting THERM Low as an Input

in Automatic Fan Speed Control Mode

THERM Timer

The ADT7467 has an internal timer to measure THERM

assertion time. For example, the THERM input can be

connected to the PROCHOT output of a Pentium 4 CPU to

measure system performance. The THERM input can also be

connected to the output of a trip point temperature sensor.

The timer is started on the assertion of the THERM input and

stopped when THERM is deasserted. The timer counts THERM

times cumulatively, that is, the timer resumes counting on the

next THERM assertion. The THERM timer continues to

accumulate THERM assertion times until the timer is read (it is

cleared upon a read) or until it reaches full scale. If the counter

reaches full scale, it stops at that reading until cleared.

The 8-bit THERM timer register (0x79) is designed such that

Bit 0 is set to 1 upon the first THERM assertion. Once the

cumulative THERM assertion time exceeds 45.52 ms, Bit 1 of

the THERM timer is set and Bit 0 becomes the LSB of the timer

with a resolution of 22.76 ms (see Figure 31).

It is important to be aware of the following when using the

THERM timer.

After a THERM timer is read (Register 0x79), the following

occurs:

•

The contents of the timer are cleared upon a read.

•

The F4P bit (Bit 5) of Interrupt Status Register 2 must be

cleared, assuming that the THERM timer limit has been

exceeded.

If the THERM timer is read during a THERM assertion, the

following occurs:

•

The contents of the timer are cleared.

•

Bit 0 of the THERM timer is set to 1 because a THERM

assertion is occurring.

•

The THERM timer increments from 0.

•

If the THERM timer limit (Register 0x7A) is 0x00, the F4P

bit is set.

THERM

TIMER

(REG. 0x79)

THERM ASSERTED

≤

22.76ms

7 6 5

321 0

0 0 0

000 1

THERM

TIMER

(REG. 0x79)

THERM ASSERTED

≥

45.52ms

7 6 5

321 0

0 0 0

001 0

THERM

TIMER

(REG. 0x79)

THERM ASSERTED ≥ 113.8ms

(91.04ms + 22.76ms)

7 6 5

321 0

0 0 0

010 1

THERM

ACCUMULATE THERM LOW

ASSERTION TIMES

THERM

ACCUMULATE THERM LOW

ASSERTION TIMES

Figure 31.Understanding the THERM Timer

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