Guide

Thermal and Mechanical Design
48 Intel® Xeon® Processor E7 2800/4800/8800 v2 Product Family
Thermal/ Mechanical Specifications and Design Guide
2.3.2 Fan Speed Control
Fan speed control (FSC) techniques to reduce system-level acoustic noise are a
common practice in server designs. The fan speed is one of the parameters that
determines the amount of airflow provided to the thermal solution. Additionally, airflow
is proportional to a thermal solution’s performance, which consequently determines the
T
CASE
of the processor at a given power level. Because the T
CASE
of a processor is an
important parameter in determining the long-term reliability of a processor, the FSC
implemented in a system directly correlates to the processor’s ability to meet the
Thermal Profile. For this purpose, the parameter called T
CONTROL
, as explained in the
datasheet, is to be used in FSC designs to ensure that the long-term reliability of the
processor is met while keeping the system-level acoustic noise down. Figure 2-26
depicts the relationship between T
CONTROL
and FSC methodology.
When DTS (Digital Temperature Sensor) value is less than Tcontrol, the thermal profile
can be ignored. The DTS value is a relative temperature to PROCHOT which is the
maximum allowable temperature before the thermal control circuit is activated. In this
region, the DTS value can be utilized to not only ensure specification compliance but
also to optimize fan speed control resulting in the lowest possible fan power and
acoustics under any operating conditions. When DTS goes above Tcontrol, fan speed
must increase to bring the sensor temperature below Tcontrol or to ensure compliance
with the Tcase profile.
Figure 2-26. T
CONTROL
and Fan Speed Control
Thermal Profile
Tcase
Power
TDP
Tcase_Max
Tcase @
Tcontrol
Pcontrol
Thermal Profile
Tcase
Power
TDP
Tcase_Max
Tcase @
Tcontrol
Pcontrol
Table 2-14. Fan Speed Control, T
CONTROL
and DTS Relationship
Condition FSC Scheme
DTS ≤ T
CONTROL
FSC can adjust fan speed to maintain DTS ≤ T
CONTROL
(low acoustic region).
DTS
> T
CONTROL
FSC should adjust fan speed to keep T
CASE
at or below the Thermal Profile
specification (increased acoustic region).