Enhancing System Acoustics - Analog Devices ADT7473 Manual

The operating point for the processor can be determined by
allowing the current temperature to be copied to the operating
point register when the PROCHOT output pulls the THERM
input low on the ADT7473. This gives the maximum
temperature at which the Pentium 4 can run before clock
modulation occurs.
Enabling the THERM Trip Point as the Operating Point
Bits <4:2> of dynamic T Control Register 1 (Reg. 0x36)
MIN
enable/disable THERM monitoring to program the operating
point.
Dynamic T Control Register 1 (0x36)
MIN
<2> PHTR2 = 1, copies the Remote 2 current temperature to
the Remote 2 operating point register, if THERM is asserted.
The operating point contains the temperature at which THERM
is asserted. This allows the system to run as quietly as possible
without affecting system performance.
PHTR2 = 0, ignores any THERM assertions. The Remote 2
operating point register reflects its programmed value.
<3> PHTL = 1, copies the local current temperature to the local
temperature operating point register if THERM is asserted. The
operating point contains the temperature at which THERM is
asserted. This allows the system to run as quietly as possible
without affecting system performance.
PHTL = 0, ignores any THERM assertions. The local
temperature operating point register reflects its programmed
value.
<4> PHTR1 = 1, copies the Remote 1 current temperature to
the Remote 1 operating point register if THERM is asserted.
The operating point contains the temperature at which THERM
is asserted. This allows the system to run as quietly as possible
without affecting system performance.
PHTR1 = 0, ignores any THERM assertions. The Remote 1
operating point register reflects its programmed value.
Enabling Dynamic T Control Mode
MIN
Bits <7:5> of dynamic T control Register 1 (Reg. 0x36)
MIN
enable/disable dynamic T
MIN
channels.
control on the temperature
Dynamic Control Register 1 (0x36)
TMIN
<5> R2T = 1, enables dynamic T
temperature channel. The chosen T
adjusted based on the current temperature, operating point, and
high and low limits for this zone.
R2T = 0, disables dynamic T
is not adjusted and the channel behaves as described in the
Automatic Fan Control Overview section.
<6> LT = 1, enables dynamic T
temperature channel. The chosen T
adjusted based on the current temperature, operating point, and
high and low limits for this zone.
LT = 0, disables dynamic T
not adjusted and the channel behaves as described in the
Automatic Fan Control Overview section.
<7> R1T = 1, enables dynamic T
temperature channel. The chosen T
adjusted based on the current temperature, operating point, and
high and low limits for this zone.
R1T = 0, disables dynamic T
is not adjusted, and the channel behaves as described in the
Automatic Fan Control Overview section.

ENHANCING SYSTEM ACOUSTICS

Automatic fan speed control mode reacts instantaneously to
changes in temperature; that is, the PWM duty cycle responds
immediately to temperature change. Any impulses in
temperature can cause an impulse in fan noise. For psycho-
acoustic reasons, the ADT7473 can prevent the PWM output
from reacting instantaneously to temperature changes.
Enhanced acoustic mode controls the maximum change in
PWM duty cycle at a given time. The objective is to prevent the
fan from cycling up and down, annoying the user.
Acoustic Enhancement Mode Overview
Figure 71 gives a top-level overview of the automatic fan control
circuitry on the ADT7473 and shows where acoustic enhance-
ment fits in. Acoustic enhancement is intended as a postdesign
tweak made by a system or mechanical engineer evaluating best
settings for the system. Having determined the optimal settings
for the thermal solution, the engineer can adjust the system
acoustics. The goal is to implement a system that is acoustically
pleasing without causing user annoyance due to fan cycling. It is
important to realize that although a system might pass an
acoustic noise requirement specification (for example, 36 dB), if
the fan is annoying, it fails the consumer test.
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ADT7473
control on the Remote 2
MIN
value is dynamically
MIN
control. The T value chosen
MIN MIN
control on the local
MIN
value is dynamically
MIN
control. The T value chosen is
MIN MIN
control on the Remote 1
MIN
value is dynamically
MIN
control. The T value chosen
MIN MIN