Sensor Based Thermal Specification Design Guidance
56 Thermal/Mechanical Specifications and Design Guidelines
For a processor specification based on a T
CASE
thermal profile, when the DTS value is
equal to or greater than T
CONTROL
, the fan speed is accelerated to maximum fan speed
for the T
AMBIENT
as controlled by the thermistor in thermal solution. For the RCFH7-
1156 (DHA-A), this would be about 2150 RPM at 35 °C. This is graphically displayed as
the dashed line in Figure 7-7.
This is an improvement over the ambient unaware system but is not fully optimized for
acoustic benefit. The DTS thermal specification required Ψ
CA
and therefore the fan
speed in this scenario is 1500 RPM. This is less than thermistor controlled speed of
2150 RPM — even if the assumption is a T
AMBIENT
= 35 °C. This is graphically displayed
in Figure 7-7.
The shaded area displayed in Figure 7-7 is where DTS values are less than T
CONTROL
.
For simplicity, the graph shows a linear acceleration of the fans from T
CONTROL
- 10 to
T
CONTROL
as has been Intel’s guidance for simple fan speed control algorithms.
As the processor workload continues to increase the DTS value will increase and the
FSC algorithm will linearly increase the fan speed from the 1500 RPM at DTS = -20 to
2150 RPM at DTS value = -1.
Figure 7-7. Fan Response with T
AMBIENT
Aware FSC
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