Intel QX9770 Design Guidelines - Page 98
E.1.2, Minimum Fan Speed Set Point, Fan Speed, Fan Inlet, Temperature °C, Speed, Operating
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Figure 57. Thermistor Set Points Full Speed Legacy Fan Speed Control Variable Speed Fan (VSF) Curve Fan Speed (RPM) Min. Operating 30 38 Fan Inlet Temperature (°C) 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. 98 Thermal and Mechanical Design Guidelines