Fan Speed Control (Fsc) Design Process; Fan Speed Control Algorithm Without Tambient - Intel Core i7-800 Specifications

7.4

Fan Speed Control (FSC) design process

The next step is to incorporate the thermal solution characterization data into the
algorithms for the device controlling the fans.
As a reminder, the requirements are:
• When the DTS value is at or below T
as with prior processors.
• When DTS is above T
Ψ versus RPM to achieve the necessary level of cooling.
CA
This chapter will discuss two implementations. The first is a FSC system that is not
provided the T
current T
acoustic benefit by operating the processor closer to the thermal profile. But only the
T
AMBIENT
performance.
In the development of the FSC algorithm it should be noted that the T
expected to change at a significantly slower rate than the DTS value. The DTS value will
be driven by the workload on the processor and the thermal solution will be required to
respond to this much more rapidly than the changes in T
An additional consideration in establishing the fan speed curves is to account for the
thermal interface material performance degradation over time.
7.4.1 Fan Speed Control Algorithm without T
In a system that does not provide the FSC algorithm with the T
designer must make the following assumption:
• When the DTS value is greater than T
derived in
This is consistent past FSC guidance from Intel, to accelerate the fan to full speed when
the DTS value is greater than T
specification at DTS = T
and provide an acoustic noise reduction from the processor thermal solution.
In this example the following assumptions are made:
• T
AMBIENT
• Thermal Solution designed / validated to a 40 °C environment
• T
CONTROL
• Reference processor thermal solution (RCFH7-1156 (DHA-A))
• Below T
For a processor specification based on a T
equal to or greater than T
the reference thermal solution full speed is 3150 RPM (dashed line in
DTS thermal specification defines a required Ψ
2300 RPM. This is much less than full speed even when assuming the T
(solid line in
54
CONTROL
information and a FSC system that is provided data on the
AMBIENT
. Either method will result in a thermally compliant solution and some
AMBIENT
aware FSC system can fully use the specification for optimized acoustic
Section 7.3.1.
CONTROL
CONTROL
= 40 °C
= -20
the fan speed is slowed down as in prior products
CONTROL
CONTROL
Figure 7-6). The shaded area displayed in
Sensor Based Thermal Specification Design Guidance
, the fans can be slowed down — just
CONTROL
, FSC algorithms will use knowledge of T
, the T
CONTROL AMBIENT
. As will be shown below, the DTS thermal
can reduce some of the over cooling of the processor
thermal profile, when the DTS value is
CASE
, the fan speed must be accelerated to full speed. For
at T
CA CONTROL
Figure 7-6
Thermal/Mechanical Specifications and Design Guidelines
AMBIENT
is
AMBIENT
.
AMBIENT
Data
AMBIENT
information, the
AMBIENT
is at boundary condition
Figure 7-6). The
and the fan speed is
= 40 °C
AMBIENT
is where DTS values
and