ADT7467 Analog Devices, Inc., ADT7467 Datasheet - Page 35

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

AUTOMATIC FAN CONTROL OVERVIEW
The ADT7467 can automatically control the speed of fans based
on the measured temperature. This is done independently of
CPU intervention once initial parameters are set up.
The ADT7467 has a local temperature sensor and two remote
temperature channels that can be connected to a CPU on-chip
thermal diode (available on Intel Pentium class and other
CPUs). These three temperature channels can be used as the
basis for automatic fan speed control to drive fans using pulse
width modulation (PWM).
Automatic fan speed control reduces acoustic noise by
optimizing fan speed according to accurately measured
temperature. Reducing fan speed can also decrease system
current consumption. The automatic fan speed control mode is
very flexible due to the number of programmable parameters,
including T
temperature channel and, therefore, for a given fan are critical
because they define the thermal characteristics of the system.
Thermal validation of the system is one of the most important
steps in the design process; therefore, these values should be
selected carefully.
MIN
and T
REMOTE 1
REMOTE 2
RANGE
LOCAL
TEMP
TEMP
TEMP
. The T
THERMAL CALIBRATION
THERMAL CALIBRATION
THERMAL CALIBRATION
MIN
T
T
T
MIN
MIN
MIN
and T
RANGE
T
T
T
RANGE
RANGE
RANGE
values for a
Figure 49. Automatic Fan Control Block Diagram
100%
100%
100%
0%
0%
0%
MUX
Rev. A| Page 35 of 80
PWM
PWM
PWM
MIN
MIN
MIN
Figure 49 shows a top-level overview of the automatic fan
control circuitry on the ADT7467. From a systems-level
perspective, up to three system temperatures can be monitored
and used to control three PWM outputs. The three PWM
outputs can be used to control up to four fans. The ADT7467
allows the speed of four fans to be monitored. Each temperature
channel has a thermal calibration block, allowing the designer
to individually configure the thermal characteristics of each
temperature channel. For example, one can decide to run the
CPU fan when CPU temperature increases above 60°C and to
run a chassis fan when the local temperature increases above
45°C. At this stage, the designer has not assigned these thermal
calibration settings to a particular fan drive (PWM) channel.
The right side of Figure 49 shows controls that are fan-specific.
The designer can individually control parameters such as
minimum PWM duty cycle, fan speed failure thresholds, and
even ramp control of the PWM outputs. Therefore, automatic
fan control ultimately allows gracefully changing fan speed so
that it is less perceptible to the system user.
ENHANCEMENT)
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
TACHOMETER 2
MEASUREMENT
ENHANCEMENT)
TACHOMETER 3
MEASUREMENT
(ACOUSTIC
(ACOUSTIC
(ACOUSTIC
CONTROL
CONTROL
CONTROL
RAMP
RAMP
AND 4
RAMP
GENERATOR
GENERATOR
GENERATOR
CONFIG
CONFIG
CONFIG
PWM
PWM
PWM
PWM
PWM
PWM
PWM1
TACH1
PWM2
TACH2
PWM3
TACH3
ADT7467