Altera PowerPlay Early Power Estimator - Manual (Page 60)

3–42 Altera Corporation
PowerPlay Early Power Estimator For Stratix II, Stratix II GX & HardCopy II January 2007
Power Analysis
If you want the PowerPlay Early Power Estimator spreadsheet thermal
model to take the junction-to-board thermal resistance (
θ
JB
) into
consideration, set the Board Thermal Model to either “Typical” or
“Custom.” A Typical board thermal model sets
θ
JB
to a value based on the
package and device selected. If you choose a Custom board thermal
model, you must specify a value for
θ
JB
. If you do not want the PowerPlay
Early Power Estimator spreadsheet thermal model to take the
θ
JB
resistance into consideration, set the Board Thermal Model to “None
(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:
(T
J
– T
A
)
θ
JA
(T
J
– T
B
)
θ
JB
+ P =