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Acoustic Fan Speed Control
R
54
Thermal/Mechanical Design Guide
Chapter 5 discussed in detail the reference thermal solution, including the target
Ψ
CA
, fan speed
and temperatures to ensure that T
C-MAX
is not exceeded for TDP power at a given ambient
temperature. The resulting variable speed fan (VSF) curve is the upper limit on fan speed.
The benefit of this upper limit will become more apparent when the fan speed controller is
responding to the on-die thermal diode temperatures.
Figure 16. Thermistor Set Points
F
an S
pee
d
(RPM
)
Fan Inlet
Temperature (°C)
Full
Speed
30
38
Min.
Operating
Variable Speed Fan (VSF) Curve
F
an S
pee
d
(RPM
)
Fan Inlet
Temperature (°C)
Full
Speed
30
38
Min.
Operating
Variable Speed Fan (VSF) Curve
6.2.3
Minimum Fan Speed Set Point
The final aspect of thermal solution design is to determine the minimum speed at which the fan
will be allowed to operate. This value can be driven by the cooling requirements for another
portion of the design, such as the processor voltage regulator, or by functional limits of the fan
design.
Per the
Fan Specification for 4 wire PWM Controlled Fans,
there are three possible options to
consider:
•
Type A: The fan will run at minimum RPM for all PWM duty cycle values less than
minimum duty cycle. This would be programmed into the fan controller located on the fan
hub. It can not be overridden by the external fan speed control.
•
Type B: The fan will run at minimum RPM for all non-zero PWM duty cycle values less than
minimum duty cycle and the fan will turn off at 0% PWM duty cycle.
•
Type C: The fan will stop running when the current provided to the motor windings is
insufficient to support commutation. The fan would turn off at 0% PWM duty cycle input.
For the reference thermal solution, Type A was implemented.
Summary of Contents for 640 - Pentium 4 640 3.2GHz 800MHz 2MB Socket 775 CPU
Page 14: ...Introduction R 14 Thermal Mechanical Design Guide ...
Page 38: ...Thermal Management Logic and Thermal Monitor Feature R 38 Thermal Mechanical Design Guide ...
Page 52: ...Intel Thermal Mechanical Reference Design Information R 52 Thermal Mechanical Design Guide ...
Page 60: ...Acoustic Fan Speed Control R 60 Thermal Mechanical Design Guide ...
Page 72: ...Heatsink Clip Load Metrology R 72 Thermal Mechanical Design Guide ...
Page 99: ...Mechanical Drawings R Thermal Mechanical Design Guide 99 Figure 50 Reference Fastener Sheet 1 ...
Page 103: ...Mechanical Drawings R Thermal Mechanical Design Guide 103 Figure 54 Clip Heatsink Assembly ...