Altera PowerPlay Early Power Estimator User Manual
Page 50
3–36
Altera
Corporation
PowerPlay Early Power Estimator For Arria GX FPGAs
May 2008
Power Analysis
(conservative).” In this case, the path through the board is not considered
for power dissipation and a more conservative thermal power estimate is
obtained.
The junction-to-ambient thermal resistance (
θ
JA
) is determined by the
addition of the junction-to-case thermal resistance (
θ
JC
), the case-to-heat
sink thermal resistance (
θ
CS
), and the heat sink-to ambient thermal
resistance (
θ
SA
).
θ
JA
=
θ
JC
+
θ
CS
+
θ
SA
Based on the device, package, airflow, and the heat sink solution selected
in the main input parameters, the PowerPlay Early Power Estimator
spreadsheet determines the junction-to-ambient thermal resistance (
θ
JA
).
If you are using a low, medium, or high profile heat sink, select the
airflow from the options of still air and air flow rates of 100 lfm (0.5 m/s),
200 lfm (1.0 m/s), and 400 lfm (2.0 m/s). If you are using a custom heat
sink, enter the heat sink-to-ambient thermal resistance (
θ
SA
). The airflow
should also be incorporated into
θ
SA
. Therefore, the Airflow parameter is
not applicable in this case. Obtain these values from the heat sink
manufacturer.
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
,
θ
JB
, and the ambient, board and junction temperature using
the following equation:
shows the thermal analysis, including the junction
temperature (T
J
), total
θ
JA
,
θ
JB
, and the maximum allowed T
A
values. For
details on the values of the thermal parameters not listed, click the
Details…
button.
(T
J
– T
A
)
θ
JA
(T
J
– T
B
)
θ
JB
+
P =