Intel Xeon Processor with 800 MHz System Bus Thermal/Mechanical Design Guide

16 Intel® Xeon™ Processor with 800 MHz System Bus Thermal/Mechanical Design Guidelines
Thermal/Mechanical Reference Design
The higher end point of the Thermal Profile represents the processor’s TDP and the associated
maximum case temperature (T
CASE
MAX). The lower end point of the Thermal Profile represents
the power value (Pcontrol_base) and the associated case temperature
(T
CASE
MAX@Pcontrol_base) for the lowest possible theoretical value of T
CONTROL
(see
Chapter 2.2.2). The slope of the Thermal Profile line represents the case-to-ambient resistance of
the thermal solution with the y-intercept being the local processor ambient temperature. The slope
of the Thermal Profile is constant between P
CONTROL BASE
and TDP, which indicate that all
frequencies of a processor defined by the Thermal Profile, will require the same heatsink case-to-
ambient resistance.
In order to satisfy the Thermal Profile specification, a thermal solution must be at or below the
Thermal Profile line for the given processor when its diode temperature is greater than T
CONTROL
(refer to Chapter 2.2.2). The Thermal Profile allows the customers to make a trade-off between
the thermal solution case-to-ambient resistance and the processor local ambient temperature that
best suits their platform implementation (refer to Chapter 2.3.3). There can be multiple
combinations of thermal solution case-to-ambient resistance and processor local ambient
temperature that can meet a given Thermal Profile. If the case-to-ambient resistance and the local
ambient temperature are known for a specific thermal solution, the Thermal Profile of that solution
can easily be plotted against the Thermal Profile specification. As explained above, the case-to-
ambient resistance represents the slope of the line and the processor local ambient temperature
represents the y-axis intercept. Hence the T
CASE
values of a specific solution can be calculated at
the TDP and Pcontrol_base power levels. Once these points are determined, they can be joined by
a line, which represents the Thermal Profile of the specific solution. If that line stays at or below
the Thermal Profile specification, then that particular solution is deemed as a compliant solution.
2.2.2 T
CONTROL
Definition
T
CONTROL
is a temperature specification based on a temperature reading from the processor’s
thermal diode. T
CONTROL
defines the lower end of the Thermal Profile line for a given processor,
and it can be described as a trigger point for fan speed control implementation. The value for
T
CONTROL
is calibrated in manufacturing and configured for each processor individually. For the
Figure 2-2. Thermal Profile Diagram
Pcontrol_Base TDP
T
CASE
MAX
Power
Thermal Profile
@Pcontrol_Base
T
CASE
MAX
T
CASE
T
CASE
MAX @
Pcontrol_base
T
CASE
MAX
Pcontrol_Base TDP
T
CASE
MAX
Power
Thermal Profile
@Pcontrol_Base
T
CASE
MAX
T
CASE
T
CASE
MAX @
Pcontrol_base
T
CASE
MAX