Intel E2180 Design Guide - Page 115
Combining Thermistor and On-Die Thermal, Sensor Control, Interaction of Thermal Profile and T
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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 ΨCA 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 Full Speed Variable Speed Fan (VSF) Curve 100 % Fan Speed (RPM) Fan Speed (% PWM Duty Cycle) Min. Operating Fan Speed Operating Range with FSC Min % E.4 30 34 38 Inlet Temperature (°C) Interaction of Thermal Profile and TCONTROL The processor thermal specification is comprised of the two parameters, TCONTROL and 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 TCONTROL ⎯ When the thermal solution can maintain the thermal sensor temperature to less than TCONTROL then the fan speed can be reduced. • On-die Thermal Sensor greater than TCONTROL ⎯ The TC must be maintained at or below the Thermal Profile for the measured power dissipation. Thermal and Mechanical Design Guidelines 115