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

Legacy Fan Speed Control
Thermal and Mechanical Design Guidelines 107
Appendix E Legacy Fan Speed
Control
A motherboard design may opt to use a SIO or ASIC based fan speed control device
that uses the existing look up or state based fan speed control.
The fan speed control implementations consist of the following items
• A motherboard designed with a fan speed controller with the following
functionality:
⎯ PWM fan control output
⎯ Remote Digital thermal sensor measurement capability over the PECI bus for
Intel
®
Core™2 Duo desktop processor E6000/E4000 sequence and Intel
®
Pentium
®
Dual Core processor E2000 sequence.
⎯ SST thermal sensor to measure the on-die thermal diode for all earlier
processors in the 775-land LGA package
• A motherboard with a 4 pin fan header for the processor heatsink fan.
• Processor heatsink with 4–wire PWM controlled Fan.
A thermistor in the fan hub is recommended, but not a requirement. The reference
solution and the Boxed Processor will implement a thermistor into the design.
The following sections discuss the necessary steps to implement Legacy Fan Speed
Control.
Note: For the rest of this section the term “on-die thermal sensor” will be used
interchangeably for the Digital thermal sensor or on-die thermal diode. On-die thermal
diode will only be used when required for clarity.
E.1 Thermal Solution Design
The first step is to select or design a processor thermal solution that meets the
thermal profile for the processor. See Section
2.2.2 for the definition of the thermal
profile and consult the processor datasheet for the specific values.
The designer needs to ensure that when the heatsink fan is operating at full speed the
thermal solution will meet the T
C-MAX
limits at TDP. The slope of the thermal profile will
allow the designer to make tradeoffs in thermal performance versus the inlet
temperature to the processor fan heatsink.
E.1.1 Determine Thermistor Set Points
A thermistor implemented in the hub of a fan is a first level of fan speed control. It
provides an easy and cost effective means to begin acoustic noise reduction. It will, by
design, run the fan at an appropriate speed based on the ambient conditions.
Chapter
5 and 6 discussed in detail the reference thermal solution, including the
target Ψ
CA
, and fan speed based on temperature to ensure that T
C-MAX
is not exceeded