Enhancing System Acoustics - Analog Devices dBCool ADT7473 Manual

Enabling the THERM Trip Point as the Oper
Bits [4:2] of Dynamic T Control Register 1 (0x36)
MIN
enable/disable THERM monitoring to program the operating
point.
Dynamic T Control Register 1 (0x36)
MIN
Bit [4] PHTR2 = 1, copies the Remote 2 current temperature to
the Remote 2 operating point register, if THERM is asserted.
The operating point contains the tempera
is asserted. This allows the system to run as quietly as p
with out affecting system perfor
PHT R2 = 0, ignores any THERM assertions. The Remote 2
oper ating point register reflects its p
Bit [3] P HTL = 1, copies the loca
loca l temperature operating poin
asse rted. The operating point co
THE RM is asserted. This allows the system to run as quietly as
poss ible without affecting system p
PHTL = 0, ignores any THERM assertions. The local
temperature operating point register reflects its prog
valu e.
Bit [ 2] PHTR1 = 1, copies the Rem
the R emote 1 operating point regis
The operating point contains th
is as serted. This allows the system
with out affecting system performa
PHT R1 = 0, ignores any THERM assertions. The Remote 1
oper ating point register reflects its p
Enabling Dynamic T Control Mode
MIN
Bits [7:5] of the Dynamic T
MIN
enab le/disable dynamic T
MIN
chan nels.
ating Point
ture at which THERM
ossible
mance.
rogrammed value.
l current temperature to the
t register if THERM is
ntains the temperature at which
erformance.
rammed
ote 1 current temperature to
ter if THERM is asserted.
e temperature at which THERM
to run as quietly as possible
nce.
rogrammed value.
C ontrol Register 1 (0x36)
contr ol on the temperature
Dynamic
TMIN
Bit [7] 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.
Bit [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.
Bit [5] 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.
Rev. A | Page 53 of 76
Control Register 1 (0x36)
control on the Remote 2
MIN
value is dynamically
MIN
control. The T
MIN
control on the local
MIN
value is dynamically
MIN
control. The T
MIN
control on the Remote 1
MIN
value is dynamically
MIN
control. The T
MIN
ADT7473
value chosen
MIN
value chosen is
MIN
value chosen
MIN