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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:
1. What ADT7476A 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 ADT7476A offers multifunctional pins that
can be reconfigured to suit different system
requirements and physical layouts. These
multifunction pins are software programmable.
REMOTE1 =
AMBIENT TEMP
LOCAL =
VRM TEMP
REMOTE2 =
CPU TEMP
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THERMAL CALIBRATION
100%
0%
T
T
MIN
RANGE
THERMAL CALIBRATION
100%
MUX
0%
T
T
MIN
RANGE
THERMAL CALIBRATION
100%
0%
T
T
MIN
RANGE
Figure 48. Hardware Configuration Example
www.onsemi.com
ADT7476A
2. How many fans are supported in system, three or
four?
This influences the choice of whether to use the
TACH4 pin or to reconfigure it for the THERM
function.
3. Is the CPU fan to be controlled using the
ADT7476A, or will the CPU fan run at full speed
100% of the time?
If run at 100%, this frees up a PWM output, but
the system is louder.
4. Where will the ADT7476A be physically located
in the system?
This influences the assignment of the temperature
measurement channels to particular system
thermal zones. For example, locating the
ADT7476A close to the VRM controller circuitry
allows the VRM temperature to be monitored
using the local temperature channel.
PWM
MIN
PWM
CONFIG
PWM
S
GENERATOR
ENHANCEMENT)
TACHOMETER1
MEASUREMENT
PWM
MIN
PWM
CONFIG
PWM
S
GENERATOR
ENHANCEMENT)
TACHOMETER2
MEASUREMENT
PWM
MIN
PWM
CONFIG
PWM
S
GENERATOR
ENHANCEMENT)
TACHOMETER3
AND 4
MEASUREMENT
35
RAMP
CONTROL
PWM1
(ACOUSTIC
TACH1
CPU FAN SINK
RAMP
CONTROL
PWM2
(ACOUSTIC
TACH2
FRONT CHASSIS
RAMP
CONTROL
PWM3
(ACOUSTIC
TACH3
REAR CHASSIS
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