Intel QX9770 Design Guidelines - Page 56
CPU maximum current draw capability, at 35C external ambient, Heat Exchanger Fan Speed PWM - desktops
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LGA775 Socket Heatsink Loading Using the cooling approach on the Intel D975XBX2 Desktop Board the CPU current draw vs. heat exchanger fan speed is shown in Figure 20 and Table 9 as well as the performance of not having this cooling feature. This was measured as the maximum current draw before the VR circuitry reaches its maximum temperature and asserts the PROCHOT# signal. The socket has a maximum temperature specification to maintain proper electrical performance at the contacts. Based on this temperature the current capability is slightly reduced but still shows improved capability of over 20 A at 100% speed over not having this feature. Figure 20. CPU Maximum Current Draw for Heat Exchanger Fan Speed CPU Current (A) 190 180 170 160 150 140 130 120 110 100 0% CPU maximum current draw capability at 35C external ambient VR/Socket Cooling Feature No Cooling Feature 20% 40% 60% 80% 100% Heat Exchanger Fan Speed (PWM) 120% Table 9. Maximum Estimated Processor Current Capability at 35 ºC External Ambient Fan Speed (PWM) 25% - VR Requirements 60% - VR Requirements 100% - VR Requirements 100% - Socket Requirements(1) Max. Current Draw for Heat Exchanger with VR and Socket Airflow Cooling Feature (A) 115 150 180 165 Max. Current Draw for Heat Exchanger and fan with no Cooling Feature (A) 105 120 150 140 NOTES: 1. Socket temperature requirement is based on the maximum temperature necessary for end of life socket electrical performance § 56 Thermal and Mechanical Design Guidelines