ADT7467 Analog Devices, Inc., ADT7467 Datasheet - Page 57

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

ENHANCING SYSTEM ACOUSTICS
Automatic fan speed control mode reacts instantaneously to
changes in temperature, that is, the PWM duty cycle immediately
responds to temperature change. Any impulses in temperature
can cause an impulse in fan noise. For psychoacoustic reasons,
the ADT7467 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 repeatedly
cycling up and down, annoying the user.
AMBIENT TEMP
REMOTE 2 =
REMOTE 1 =
VRM TEMP
CPU TEMP
LOCAL =
Figure 81. Acoustic Enhancement Smoothes Fan Speed Variations in Automatic Fan Speed Control
THERMAL CALIBRATION
THERMAL CALIBRATION
THERMAL CALIBRATION
T
T
T
MIN
MIN
MIN
T
T
T
RANGE
RANGE
RANGE
100%
100%
100%
0%
0%
0%
MUX
Rev. A| Page 57 of 80
PWM
PWM
PWM
MIN
MIN
MIN
ACOUSTIC ENHANCEMENT MODE OVERVIEW
Figure 81 shows a top-level overview of the ADT7467 automatic
fan control circuitry and where acoustic enhancement fits in.
Acoustic enhancement is intended as a postdesign tweak made
by a system or mechanical engineer evaluating the 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
and does not cause 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),
it fails the consumer test if the fan is annoying.
ENHANCEMENT
ACOUSTIC
ENHANCEMENT)
ENHANCEMENT)
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
TACHOMETER 2
MEASUREMENT
MEASUREMENT
TACHOMETER 3
(ACOUSTIC
(ACOUSTIC
(ACOUSTIC
CONTROL
CONTROL
CONTROL
RAMP
RAMP
RAMP
AND 4
GENERATOR
GENERATOR
GENERATOR
CONFIG
CONFIG
CONFIG
PWM
PWM
PWM
PWM
PWM
PWM
PWM1
TACH1
PWM2
TACH2
PWM3
TACH3
FRONT CHASSIS
REAR CHASSIS
CPU FAN SINK
ADT7467