ATX Thermal/Mechanical Design Information
60 Thermal and Mechanical Design Guidelines
T
CONTROL
specifications described in Section 2.2.3. Intel recommendation is to use the
fan with 4 Wire PWM Controlled to implement fan speed control capability based
digital thermal sensor temperature. Refer to Chapter
7 for further details.
Note: Appendix G gives detailed fan performance for the Intel reference thermal solutions
with 4 Wire PWM Controlled fan.
6.2.3 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
T
C
requirement for the processor is met at the targeted altitude.
6.2.4 Heatsink Thermal Validation
Intel recommends evaluation of the heatsink within the specific boundary conditions
based on the methodology described Section
6.3.
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 6.6).
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.
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