sc3200 Advanced Micro Devices, sc3200 Datasheet - Page 440

• Manufacturer Part Number: sc3200
• Description: Geode-tm Sc3200 Processor
• Manufacturer: Advanced Micro Devices

10.1.1
Table 10-2 on page 439 shows the maximum allowed ther-
mal resistance of a heatsink for particular operating envi-
ronments. The calculated values, defined as θ
represent the required ability of a particular heatsink to
transfer heat generated by the SC3200 processor from its
case into the air, thereby maintaining the case temperature
at or below 85°C. Because θ
resistivity, it is inversely proportional to the heatsinks ability
to dissipate heat or its thermal conductivity.
Note: A “perfect” heatsink would be able to maintain a
Looking at Table 10-2, it can be seen that as ambient tem-
perature (T
consumption of the processor (P) increases, θ
decreases. Thus, the ability of the heatsink to dissipate
thermal energy must increase as the processor power
increases and as the temperature inside the enclosure
increases.
While θ
not typically specified in terms of a single θ
because the thermal resistivity of a heatsink is not constant
across power or temperature. In fact, heatsinks become
slightly less efficient as the amount of heat they are trying
to dissipate increases. For this reason, heatsinks are typi-
cally specified by graphs that plot heat dissipation (in
watts) vs. mounting surface (case) temperature rise above
ambient (in °C). This method is necessary because ambi-
ent and case temperatures fluctuate constantly during nor-
mal operation of the system. The system designer must be
careful to choose the proper heatsink by matching the
required θ
device under the entire range of operating conditions in
order to make sure that the maximum case temperature
(from Table 9-3 on page 370) is never exceeded. To
choose the proper heatsink, the system designer must
make sure that the calculated θ
(shaded area). The curve itself defines the minimum tem-
perature rise above ambient that the heatsink can main-
tain.
Figure 10-1 is an example of a particular heatsink under
consideration
440
CA
case temperature equal to that of the ambient air
inside the system chassis.
50
40
30
20
10
Heatsink Considerations
0
is a useful parameter to calculate, heatsinks are
CA
Figure 10-1. Heatsink Example
A
) increases, θ
θ
with the thermal dissipation curve of the
CA = 45/5 = 9
2
Revision 5.1
Heat Dissipated - Watts
4
CA
decreases, and that as power
CA
CA
is a measure of thermal
6
θ
falls above the curve
CA = 45/9 = 5
8
CA
.This is
10
CA
CA
,
Example 1
Assume P (max) = 5W and T
Therefore:
The heatsink must provide a thermal resistance below 9°C/
W. In this case, the heatsink under consideration is more
than adequate since at 5W worst case, it can limit the case
temperature rise above ambient to 40°C (θ
Example 2
Assume P (max) = 9W and T
Therefore:
In this case, the heatsink under consideration is NOT ade-
quate to limit the case temperature rise above ambient to
45°C for a 9W processor.
For more information on thermal design considerations or
heatsink properties, refer to the Product Selection Guide
of any leading vendor of thermal engineering solutions.
Note: The power dissipations P used in these examples
are not representative of the power dissipation of
the SC3200 processor, which is always less than 4
Watts.
θ
θ
θ
θ
θ
θ
CA
CA
CA
CA
CA
CA
= 9
= 5
=
=
=
=
AMD Geode™ SC3200 Processor Data Book
T
85 − 40
T
85 − 40
C
C
P
5
P
9
− T
− T
A
A
A
A
(max) = 40°C.
(max) = 40°C.
Package Specifications
CA
=8).