Intel E1400 Design Guidelines - Page 113

Fan RPM, Tdiode, Tcontrol

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Legacy Fan Speed Control Figure 7-41. Temperature Range = 5 °C Fan RPM 3500 3000 2500 2000 1500 1000 500 0 Tdiode Tcontrol Time (s) Tlow 80 75 70 65 60 55 50 45 40 An alternate would be to consider a slightly larger value such as TRANGE = 10 °C. In this case the design is trading off the acoustic margin for thermal margin. There is increased granularity in the fan speeds. Fan speed oscillation are significantly reduced Maximum fan speed is lower The rate of change of CA vs. RPM is an exponential curve with a larger decrease at the beginning of the fan acceleration than as the maximum speed is approached. By having the fan start to accelerate at a lower TSENSOR reading the thermal solution can keep up with rate of change in processor power. The rate of change in acoustics (dBA) is more linear with RPM. When comparing these two metrics the choice of a larger TRANGE value becomes a more acceptable trade off. Figure 7-42 graphs the system at the same conditions as in Figure 7-41 but TRANGE = 10 °C. Thermal and Mechanical Design Guidelines 113

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Legacy Fan Speed Control
Thermal and Mechanical Design Guidelines
113
Figure 7-41. Temperature Range = 5 °C
0
500
1000
1500
2000
2500
3000
3500
Time (s)
40
45
50
55
60
65
70
75
80
Fan RPM
Tdiode
Tcontrol
Tlow
An alternate would be to consider a slightly larger value such as T
RANGE
= 10 °C. In
this case the design is trading off the acoustic margin for thermal margin.
There is increased granularity in the fan speeds.
Fan speed oscillation are significantly reduced
Maximum fan speed is lower
The rate of change of
CA
vs. RPM is an exponential curve with a larger decrease at
the beginning of the fan acceleration than as the maximum speed is approached. By
having the fan start to accelerate at a lower T
SENSOR
reading the thermal solution can
keep up with rate of change in processor power. The rate of change in acoustics (dBA)
is more linear with RPM. When comparing these two metrics the choice of a larger
T
RANGE
value becomes a more acceptable trade off. Figure 7-42 graphs the system at
the same conditions as in Figure 7-41 but T
RANGE
= 10 °C.