Altera PowerPlay Early Power Estimator - Manual (Page 48)

3–34 Altera Corporation
PowerPlay Early Power Estimator For Arria GX FPGAs May 2008
Power Analysis
Figure 3–23. 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 3–24 shows the thermal model for the
PowerPlay Early Power Estimator without a heat sink.
Figure 3–24. 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
Using a Heat Sink
When a heat sink is used the major paths of power dissipation are from
the device through the case, thermal interface material, and heat sink.
There is also a path of power dissipation through the board. The path
through the board has much less impact than the path to air.
Figure 3–25
shows the thermal representation with a heat sink.
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