Sun Microsystems SME5224AUPA-400 User Manual
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400 MHz CPU, 4.0 MB E-Cache
UltraSPARC
™
-II CPU Module
SME5224AUPA-400
Advanced Version
July 1999
Sun Microsystems, Inc
Case Temperature Measuring Method
The relationship between case temperature and junction temperature is described in the following thermal
equation.
If Tc is known, then Tj can be calculated:
Tj = Tc + (Pd x
θ
jc)
Note: Testing is done with the worst-case power draw, software loading, and ambient air temperature.
There is good tracking between the case temperature and the heatsink temperature.
Heatsink Temperature Measuring Method
Measuring the heatsink temperature is sometimes easier than measuring the case temperature. This method
provides accurate results for most designs. If the heatsink temperature (Ts) is known then the following ther-
mal equation can be used to estimate the junction temperature:
Tj = Ts + [Pd (
θ
jc +
θ
cs)]