Intel 640 User Guide - Page 58
Minimum PWM Duty Cycle
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Acoustic Fan Speed Control R Figure 20. Temperature Range = 10 °C RPM Tdiode (C) Fan RPM 3500 3000 2500 2000 1500 1000 500 0 Tdiode Tcontrol Time (s) Tlow 80 75 70 65 60 55 50 45 40 6.3.1.2 It should be noted that having TDIODE above TCONTROL is expected for near TDP power levels and high system ambient. See Section 6.5 for additional discussion on TCONTROL versus Thermal Profile. For use with the Intel® Boxed Pentium 4 Processor in 775-Land LGA Package on the enabled reference solution, a TRANGE value of 10 °C is recommended for ATX chassis. Minimum PWM Duty Cycle The final step in determining the FSC setting is to determine the minimum PWM Duty cycle. This is the fan speed for any TDIODE < TLOW. The selection of this value is dependent on: • Acoustic target at system idle • Voltage regulator cooling For a motherboard design intending to use the Intel Boxed Pentium 4 Processor in 775-land LGA Package or the enabled reference thermal solution the recommended minimum PWM duty cycle is 30%. 58 Thermal/Mechanical Design Guide