Legacy Fan Speed Control
Thermal and Mechanical Design Guidelines
109
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
the processor
⎯
SST bus 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 will 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 heat sink 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
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
for TDP power at a given ambient temperature. The resulting variable speed fan (VSF)
curve is the upper limit on fan speed.
Summary of Contents for Celeron Dual-Core E1000 Series
Page 10: ...10 Thermal and Mechanical Design Guidelines...
Page 26: ...Processor Thermal Mechanical Information 26 Thermal and Mechanical Design Guidelines...
Page 68: ...ATX Thermal Mechanical Design Information 68 Thermal and Mechanical Design Guidelines...
Page 86: ...Heatsink Clip Load Metrology 86 Thermal and Mechanical Design Guidelines...
Page 88: ...Thermal Interface Management 88 Thermal and Mechanical Design Guidelines...
Page 120: ...Legacy Fan Speed Control 120 Thermal and Mechanical Design Guidelines...
Page 126: ...Fan Performance for Reference Design 126 Thermal and Mechanical Design Guidelines...
Page 127: ...Fan Performance for Reference Design Thermal and Mechanical Design Guidelines 127...
