Intel Core2 Duo Desktop Processor, Intel Pentium Processor, and Intel Pentium 4 Processor 6x1 Sequence

ATX Thermal/Mechanical Design Information

Thermal and Mechanical Design Guidelines 55

While the fan hub thermistor helps optimize acoustics at high processor workloads by

adapting the maximum fan speed to support the processor thermal profile, additional

acoustic improvements can be achieved at lower processor workload by using the

CONTROL

specifications described in Section 2.2.3. Intel recommendation is to use the

Fan Specification for 4 Wire PWM Controlled Fans to implement fan speed control

capability based digital thermal sensor temperature. Refer to Chapter

7 for further

details.

6.1.3 Altitude

Many companies design products that must function reliably at high altitude, typically

1,500 m [5,000 ft] or more. Air-cooled temperature calculations and measurements at

the test site elevation must be adjusted to take into account altitude effects like

variation in air density and overall heat capacity. This often leads to some degradation

in thermal solution performance compared to what is obtained at sea level, with lower

fan performance and higher surface temperatures. The system designer needs to

account for altitude effects in the overall system thermal design to make sure that the

requirement for the processor is met at the targeted altitude.

6.1.4 Heatsink Thermal Validation

Intel recommends evaluation of the heatsink within the specific boundary conditions

based on the methodology described Section

6.2 , and using a thermal test vehicle.

Testing is done on bench top test boards at ambient lab temperature. In particular, for

the reference heatsink, the Plexiglas* barrier is installed 81.28 mm [3.2 in] above the

motherboard (refer to Sections 3.3 and 6.5).

The test results, for a number of samples, are reported in terms of a worst-case mean

+ 3σ value for thermal characterization parameter using real processors (based on the

thermal test vehicle correction factors).

Note: The above 81.28 mm obstruction height that is used for testing complies with the

recommended obstruction height of 88.9 mm for the ATX form factor. However, it

would conflict with systems in strict compliance with the ATX specification which

allows an obstruction as low as 76.2 mm above the motherboard surface in Area A.

6.1.5 Fan Performance for Active Heatsink Thermal Solution

The fan power requirements for proper operation are given Table 10.

Table 10. Fan Electrical Performance Requirements

Requirement Value

Maximum Average fan current draw 1.5 A

Fan start-up current draw 2.2 A

Fan start-up current draw maximum duration 1.0 second

Fan header voltage 12 V ±5%

Tachometer output 2 pulse per revolution