Altera PowerPlay Early Power Estimator - Manual (Page 58)

3–40 Altera Corporation
PowerPlay Early Power Estimator For Stratix II, Stratix II GX & HardCopy II January 2007
Power Analysis
ambient thermal resistance paths. The first is from the device through the
case to the air and the second is from the device through the board to the
air.
Figure 3–26 shows the thermal representation without a heat sink.
Figure 3–26. Thermal Representation without Heat Sink
In the model used in the PowerPlay Early Power Estimator, power is
dissipated through the case and board. Values of
θ
JA
have been calculated
for differing air flow options accounting for the paths through the case
and through the board.
Figure 3–27 shows the thermal model for the
PowerPlay Early Power Estimator without a heat sink.
Figure 3–27. Thermal Model in the PowerPlay Early Power Estimator without a
Heat Sink
The ambient temperature does not change, but the junction temperature
changes depending on the thermal properties. Since a change in junction
temperature affects the thermal device properties used to calculate
junction temperature, calculating junction temperature is an iterative
process.
The total power is calculated based on the device resource usage which
provide
θ
JA
and the ambient, board and junction temperatures using the
following equation:
P = (T
J
- T
A
) /
θ
JA
C ase
Therm al R epresentation w ithout H eat S ink
B oard
D evice
θ
JA
Power (P)
Heat
Source
T
J
T
A
θ
JA