ADT7467 Analog Devices, Inc., ADT7467 Datasheet - Page 24

• Manufacturer Part Number: ADT7467
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

ADT7467
The user can also set up the ADT7467 so that when the
THERM pin is driven low externally, the fans run at 100%. The
fans run at 100% for the duration of the time that the THERM
pin is pulled low. This is done by setting the BOOST bit (Bit 2)
in Configuration Register 3 (Address 0x78) to 1. This only
works if the fan is already running, for example, in manual
mode when the current duty cycle is above 0x00, or in
automatic mode when the temperature is above T
temperature is below T
is set to 0x00, externally pulling THERM low has no effect. See
Figure 30 for more information.
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.
T
THERM
THERM ASSERTED TO LOW AS AN INPUT:
FANS DO NOT GO TO 100%, BECAUSE
TEMPERATURE IS BELOW T
MIN
Figure 30. Asserting THERM Low as an Input
in Automatic Fan Speed Control Mode
MIN
MIN
or if the duty cycle in manual mode
THERM ASSERTED TO LOW AS AN INPUT:
FANS DO NOT GO TO 100%, BECAUSE
TEMPERATURE IS ABOVE T
ARE ALREADY RUNNING
MIN
MIN
AND FANS
. If the
Rev. A | Page 24 of 80
The 8-bit THERM timer register (Reg. 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 read (Reg. 0x79), the following occurs:
1.
2.
If the THERM timer is read during a THERM assertion, the
following occurs:
1.
2.
3.
4.
The contents of the timer are cleared upon a read.
The F4P bit (Bit 5) of Status Register 2 must be cleared,
assuming that the THERM timer limit has been exceeded.
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 (Reg. 0x7A) is 0x00, the F4P bit
is set.
(REG. 0x79)
(REG. 0x79)
(REG. 0x79)
THERM
THERM
THERM
THERM
THERM
THERM
TIMER
TIMER
TIMER
ACCUMULATE THERM LOW
ACCUMULATE THERM LOW
Figure 31.Understanding the THERM Timer
ASSERTION TIMES
ASSERTION TIMES
0 0 0
7 6 5
0 0 0
7 6 5
0 0 0
7 6 5
0
4
0
4
0
4
0 0 0 1
3 2 1 0
0 0 1 0
3 2 1 0
0 1 0 1
3 2 1 0
THERM ASSERTED ≥ 113.8ms
(91.04ms + 22.76ms)
THERM ASSERTED
THERM ASSERTED
≤ 22.76ms
≥ 45.52ms