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®
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Intel
Pentium
III Processor in the FC-PGA2 Package Thermal Design Guidelines
Equation 2. Case to Ambient Thermal Resistance
Where:
CA
T
CASE
T
LA
TDP
CS
SA
7.2.
Thermal Solution Performance
All processor thermal solutions interface to the processor at the IHS. The system thermal solution must
adequately control the local-ambient air around the processor (T
between the processor and the local-ambient air, the more efficient the thermal solution is. The required
is dependent upon the maximum allowed processor temperature (T
CA
temperature (T
packaged processors, refer to the processor datasheet.
Use Equation 1 and Equation 2 (above) to determine a target
assumptions.
T
CASE
T
LA
TDP
CS
Solving for the equation 1 from above:
CA
Solving for equation 2 from above:
CA
SA
24
=
thermal resistance from case to local-ambient (°C/W)
=
processor case temperature (°C)
=
local-ambient temperature in chassis around processor (°C)
=
processor Thermal Design Power dissipation (W) (assume all power goes to the case)
=
case-to-sink thermal resistance (°C/W)
=
sink to local-ambient thermal resistance (°C/W)
) and the processor thermal design power (TDP). For actual specifications on FC-PGA2
LA
=
67 °C, hypothetical maximum case temperature specification
=
Assume 45°C, a typical value for desktop systems
=
Assume 30 W, hypothetical thermal design power
=
Assume 0.15 °C/W, hypothetical TIM resistance
= (T
- T
) / TDP
CASE
LA
= (67 – 45) / 30
= 0.73 °C/W
=
+
CS
SA
=
CA
CS
= 0.73
0.15
= 0.58 °C/W
=
+
CA
CS
SA
). The lower the thermal resistance
LA
CASE
and
CA
SA
), the local-ambient
using the following
249660-001
R
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