ADT7476
Rev. B | Page 38 of 72
05382-048
MUX
THERMAL CALIBRATION
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
THERMAL CALIBRATION
100%
0%
T
MIN
T
RANGE
REMOTE 1
TEMP
LOCAL
TEMP
REMOTE 2
TEMP
PWM
MIN
PWM1
TACH1
TACH2
TACH3
PWM
MIN
PWM2
PWM
MIN
PWM3
100%
PWM
GENERATOR
PWM
GENERATOR
TACHOMETER 3
AND 4
MEASUREMENT
TACHOMETER 1
MEASUREMENT
TACHOMETER 2
MEASUREMENT
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
RAMP
CONTROL
(ACOUSTIC
ENHANCEMENT)
PWM
GENERATOR
PWM
CONFIG
PWM
CONFIG
PWM
CONFIG
Figure 47. Automatic Fan Control Block Diagram
STEP 1: HARDWARE CONFIGURATION
During system design, the motherboard sensing and control
capabilities should be addressed early in the design stages.
Decisions about how these capabilities are used should involve
the system thermal/mechanical engineer. Ask the following
questions:
•
What ADT7476 functionality is used?
•
PWM2 or SMBALERT?
•
TACH4 fan speed measurement or overtemperature
THERM function?
•
2.5 V voltage monitoring or overtemperature THERM
function?
•
12 V voltage monitoring or VID5 input?
The ADT7476 offers multifunction pins that can be recon-
figured to suit different system requirements and physical
layouts. These multifunction pins are software programmable.
•
How many fans are supported in the system, three or
four? This influences the choice of whether to use the
TACH4 pin or to reconfigure it for the THERM
function.
•
Is the CPU fan to be controlled using the ADT7476,
or will the CPU fan run at full speed 100% of the
time? Running at 100% frees up a PWM output, but
the system is louder.
•
Where will the ADT7476 be physically located in the
system?
This influences the assignment of the temperature
measurement channels to particular system thermal
zones. For example, locating the ADT7476 close to the
VRM controller circuitry allows the VRM temperature
to be monitored using the local temperature channel.
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