Minimum Fan Speed Set Point; Figure 57. Thermistor Set Points - Intel QX9770 - Core 2 Extreme Quad-Core Processor Design Manual

Intel core 2 extreme processor qx6800 and intel core 2 extreme processor qx9770 thermal and mechanical design guidelines

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E.1.2

Minimum Fan Speed Set Point

The final aspect of thermal solution design is to determine the minimum speed 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 turn off the fan 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.

Variable Speed Fan (VSF) Curve

Full

Speed

Min.

Operating

Fan Inlet

Temperature (°C)

Thermal and Mechanical Design Guidelines

Legacy Fan Speed Control

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