Thermal/Mechanical Specifications and Design Guidelines 71
Boxed Processor Specifications
10.4.2 Variable Speed Fan
If the boxed processor fan heatsink 4-pin connector is connected to a 3-pin
motherboard header, it will operate as follows:
The boxed processor fan will operate at different speeds over a short range of internal
chassis temperatures. This allows the processor fan to operate at a lower speed and
noise level, while internal chassis temperatures are low. If internal chassis temperature
increases beyond a lower set point, the fan speed will rise linearly with the internal
temperature until the higher set point is reached. At that point, the fan speed is at its
maximum. As fan speed increases, so do fan noise levels. Systems should be designed
to provide adequate air around the boxed processor fan heatsink that remains cooler
then lower set point. These set points, represented in Figure 10-9 and Table 10-2, can
vary by a few degrees from fan heatsink to fan heatsink. The internal chassis
temperature should be kept below 40 ºC. Meeting the processor's temperature
specification (see Chapter 6) is the responsibility of the system integrator.
The motherboard must supply a constant +12 V to the processor's power header to
ensure proper operation of the variable speed fan for the boxed processor. Refer to
Table 10-1 for the specific requirements.
Note:
1. Set point variance is approximately ± 1 °C from fan heatsink to fan heatsink.
Figure 10-9. Boxed Processor Fan Heatsink Set Points
Table 10-2. Fan Heatsink Set Points
Boxed Processor Fan
Heatsink Set Point
(
ºC)
Boxed Processor Fan Speed Notes
X ≤ 30
When the internal chassis temperature is below or equal to this set point,
the fan operates at its lowest speed. Recommended maximum internal
chassis temperature for nominal operating environment.
1
Y = 35
When the internal chassis temperature is at this point, the fan operates
between its lowest and highest speeds. Recommended maximum internal
chassis temperature for worst-case operating environment.
-
Z ≥ 40
When the internal chassis temperature is above or equal to this set point,
the fan operates at its highest speed.
-
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