Legacy Fan Speed Control
116 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. Please refer to the Fan Specification for 4 wire PWM Controlled Fans and
Chapter
6 for complete details on the Intel enabled thermal solution.
The basics of Fan Speed Control were discussed in Chapter
7, as a review the FSC
definitions are listed in Table 7-3.
Table
7-3. FSC Definitions
Item Definition
T
SENSOR
Temperature reported from the processor on-die thermal sensor.
T
CONTROL
T
CONTROL
is the specification limit for use with the on-die thermal sensor.
Thermal
Diode Offset
Thermal Diode Offset
is the MSR value programmed into the processor with the on-
die thermal diode to account for perceived diode ideality shift.
Thermal
Diode Base
The constant published in the processor datasheet for calculating Thermal
Diode Correction Factor.
Thermal
Diode
Correction
Factor
Thermal Diode Correction Factor is the sum of the Thermal Diode Offset and
Thermal Diode Base. This value is used to compensate for temperature errors
if the diode ideality factor is near the maximum or minimum values. It is only
used for HW Monitor components that measure the on-die thermal diode using
the diode model.
T
LOW
The temperature above which the fan will begin to accelerate in response to
the on-die 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 T
CONTROL
.
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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