ADT7468 Analog Devices, Inc., ADT7468 Datasheet - Page 37

• Manufacturer Part Number: ADT7468
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

AUTOMATIC FAN CONTROL OVERVIEW
The ADT7468 can automatically control the speed of fans based
upon the measured temperature. This is done independently of
CPU intervention once initial parameters are set up.
The ADT7468 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, owing to the number of programmable para-
meters, including T
for a temperature channel and, therefore, for a given fan are
critical, because they define the thermal characteristics of the
system. The thermal validation of the system is one of the most
important steps in the design process, so these values should be
selected carefully.
REMOTE 1
REMOTE 2
MIN
LOCAL
TEMP
TEMP
TEMP
and T
RANGE
THERMAL CALIBRATION
THERMAL CALIBRATION
THERMAL CALIBRATION
T
T
T
. The T
MIN
MIN
MIN
MIN
and T
T
T
T
RANGE
RANGE
RANGE
Figure 49. Automatic Fan Control Block Diagram
100%
100%
100%
RANGE
0%
0%
0%
values
MUX
Rev. A | Page 37 of 84
PWM
PWM
PWM
MIN
MIN
MIN
Figure 49 gives a top level overview of the automatic fan control
circuitry on the ADT7468. 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 ADT7468 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
the CPU temperature increases above 60°C and 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 has
individual control over parameters such as minimum PWM
duty cycle, fan speed failure thresholds, and even ramp control
of the PWM outputs. Automatic fan control, then, ultimately
allows graceful fan speed changes that are less perceptible to the
system user.
ENHANCEMENT)
ENHANCEMENT)
ENHANCEMENT)
TACHOMETER 1
MEASUREMENT
TACHOMETER 2
MEASUREMENT
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
TACH3
PWM3
ADT7468