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Legacy Fan Speed Control
E.3
Combining Thermistor and On-Die Thermal
Sensor Control
There is no closed loop control between the FSC and the thermistor, but they work in
tandem to provide the maximum fan speed reduction. As discussed in Section E.1.1,
the thermistor establishes the VSF curve. This curve will determine the maximum fan
speed as a function of the ambient temperature and by design provides a Ψ
sufficient to meet the thermal profile. The FSC, by measuring the processor on-die
thermal sensor will command the fan to reduce speed below the VSF curve in
response to processor workload. Conversely if the processor workload increases the
FSC will command the fan via the PWM duty cycle to accelerate the fan up to the limit
imposed by the VSF curve.
Figure 7-43. On-Die Thermal Sensor and Thermistor
E.4
Interaction of Thermal Profile and T
The processor thermal specification is comprised of the two parameters, T
Thermal Profile. The minimum requirement for thermal compliance is to ensure the
thermal solution, by design, meets the thermal profile.
If the system design will incorporate acoustic speed fan control, Intel requires
monitoring the on-die thermal sensor to implement acoustic fan speed control. The
value of the on-die thermal sensor temperature determines which specification must
be met.
• On-die Thermal Sensor less than T
⎯ When the thermal solution can maintain the thermal sensor temperature to
less than T
• On-die Thermal Sensor greater than T
⎯ The T
power dissipation.
Thermal and Mechanical Design Guidelines
Variable Speed Fan (VSF) Curve
Variable Speed Fan (VSF) Curve
Full
Full
Speed
Speed
Min.
Min.
Operating
Operating
30
30
then the fan speed can be reduced.
CONTROL
must be maintained at or below the Thermal Profile for the measured
C
Fan Speed
Fan Speed
Operating Range
Operating Range
with FSC
with FSC
38
38
34
34
Inlet Temperature (°C)
Inlet Temperature (°C)
CONTROL
CONTROL
CA
100 %
100 %
Min %
Min %
CONTROL
and
CONTROL
115
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