Thermal/Mechanical Specifications and Design Guidelines
75
Sensor Based Thermal Specification Design Guidance
8.4.4
Fan Speed Control Implementation Details
Most fan controllers allow programming a few
“temperature versus PWM”
or
“
temperature v.s RPM”
points for fan speed control and do a linear interpolation
determine the
CA
requirements at T
CONTROL
and
at DTS = -1. From the thermal solution performance characteristics (RPM versus
CA)
find equivalent RPM and PWM.
give an example of how a fan speed control
table may look like for processor cooling needs. DTS 1.1 only specify the thermal
performance needed at T
CONTROL
and at DTS = -1. All the other points can be defined
as needed based on rest of the platform cooling needs.
Notes:
1.
This table is for illustration purposes only. PWM% and RPM numbers will vary based on system thermal
solution for the required
CA targets.
For a typical chassis that has Trise lower than 10C, based on the reference thermal
solution data, a fan speed of 1050 RPM will give the needed
CA
at T
CONTROL
. A
maximum fan speed of 3150 RPM will be programmed for DTS = -1. As the processor
workload continues to increase the DTS value will increase and the FSC algorithm will
linearly increase the fan speed from the 1050 RPM at DTS = -20 to fans full speed at
DTS = -1.
shows a comparison chart from this tool for various fan speed control
options including DTS 1.1.
In this example the following assumptions are made:
• Operating T
AMBIENT
= 35 °C
• Thermal Solution designed / validated to a 40 °C ambient max as used in the
example in
Reference processor thermal solution (RCFH7-1156
(DHA-A))
• T
CONTROL
= -20
• For DTS 1.0 the FSC device has access to T
AMBIENT
data
• Below T
CONTROL
the fan speed is slowed down to minimum as in prior products
• Power = 75W with all cores active
Table 8-2.
Fan Speed control example for 95W TDP processor
1
DTS values
Calculated Tj
(assuming
TjMax = 99C)
CA
Example PWM%
Example RPM
DTS = -59
40C
...
20%
1000
DTS = -39
60C
...
30%
1050
...
...
...
...
...
...
...
...
...
...
DTS = -20
79C
0.564
40%
1100
DTS = -1
98C
0.343
100%
3150
Содержание 2ND GENERATION CORE PROCESSOR FAMILY DESKTOP - THERMAL MECHANICAL S AND DESIGN GUIDELINES 01-2011
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