Legacy Fan Speed Control
104 Thermal and Mechanical Design Guidelines
To use all of the features in the Intel reference heatsink design or the Boxed
Processor, system integrators should verify the following functionality is present in the
board design. Refer to the Fan Specification for 4 wire PWM Controlled Fans and
Chapter
5 for complete details on the Intel enabled thermal solution.
The FSC definitions are listed in
Table 12.
Table 12. FSC Definitions
Item Definition
T
SENSOR
Temperature reported from the processor digital thermal sensor.
T
CONTROL
T
CONTROL
is the specification limit for use with the digital thermal sensor
T
LOW
The temperature above which the fan will begin to accelerate in response to the
digital thermal sensor temperature.
Hysteresis The number of degrees below T
CONTROL
the fans will remain on before slowing
down.
T
HIGH
The temperature at which the fan is operating at full speed (100% PWM Duty
Cycle). By specification this is Tcontrol.
All Fans ON The processor temperature at which all fans in the system are increased to 100%
Duty Cycle.
Min PWM Minimum pulse width modulation (% duty cycle) that the fans will run at when
T
SENSOR
is less than T
LOW
.
Spin-up Amount of time fan is run at 100% duty cycle to overcome fan inertia.
PWM Freq The operating frequency of the PWM signal.
T
AVERAGING
The time (in seconds) that elapses while the fan is gradually sped up in response
to a processor temperature spike.
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