Guide

Intel
®
Celeron
®
D Processor for Embedded Applications Thermal Design Guide 29
Thermal Design Guidelines
4.4 Thermal Solution Requirements
The thermal performance required for the heatsink is determined by calculating the
case-to-ambient thermal resistance,
Ψ
CA
. This is a basic thermal engineering parameter that may
be used to evaluate and compare different thermal solutions. For this particular processor an
example of how
Ψ
CA
is calculated for the Intel Celeron D processor 335 as shown in Equation 3.
In this calculation, T
C max
and TDP are constant, while Ψ
CA
may vary according to the local
ambient temperature (T
LA
). Table 3 shows an example of required thermal resistances for the
thermal solution at various local ambient temperatures. The table uses the TDP from the
Intel
Celeron D Processor Datasheet
and the T
C max
.
These numbers are subject to change, and in case of conflict the
Intel Celeron D Processor
Datasheet
supercedes the TDP and T
C max
specifications in this document.
NOTE: The Ψ
CA
performance given above refers to sea level conditions and does not take into account altitude
effects such as different air density and overall heat capacity. This often leads to some degradation in
thermal solution performance compared to what is obtained at sea level, with lower fan performance
and higher surface temperatures. Companies designing products that must function reliably at high
altitude, typically 1,500 m (5,000 ft.) or more, must adapt the thermal performance targets accordingly.
The system designer needs to account for the altitude effects in the overall system thermal design to
ensure that the requirement for the processor is met at the targeted altitude
Figure 11 further illustrates the required thermal performance for the Intel Celeron D Processor 335
at different operating ambient temperatures. The thermal solution chosen to cool the processor
must have a case-to-ambient thermal resistance less than the values shown for the given local
ambient temperature.
Equation 3. Case-to-Ambient Thermal Resistance
ψ
CA
T
cmax
°CT
LA
– °C
TDP W()
-------------------------------------------
67° C 40° C–
73W
-------------------------------- 0.370
° C
W
------===
Table 3. Processor Thermal Specifications
Intel
®
Celeron
®
D Processor for Embedded
Applications
Required Thermal Resistance, Ψ
CA
(°C/W) of
Thermal Solution at T
LA
= (°C)
Processor
Number
Frequency
(GHz)
TDP
(W)
T
C
Max
(°C)
50 45 40 35 30
335 2.8 73 67 0.233 0.301 0.370 0.438 0.507