Altera PowerPlay Early Power Estimator User Manual
Page 34
3–22
Chapter 3: Using Cyclone III PowerPlay Early Power Estimator
Power Analysis
PowerPlay Early Power Estimator User Guide for Cyclone III FPGAs
© June 2009 Altera Corporation
If you want the PowerPlay Early Power Estimator thermal model to take the
JABOTTOM
thermal resistance into consideration, set the Board Thermal Model to either Typical
Board
or JEDEC (2s2p). If you do not want the PowerPlay Early Power Estimator
thermal model to take the
JA BOTTOM
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
JA TOP
is determined by the sum of the junction-to-case thermal resistance (
JC
), the
case-to-heat sink thermal resistance (
CS
), and the heat sink-to ambient thermal
resistance (
SA
):
JA TOP
=
JC
+
CS
+
SA
Based on the device, package, airflow, and heat sink solution selected in the main
input parameters, the PowerPlay Early Power Estimator determines the
junction-to-ambient thermal resistance (
JA TOP
).
If you are using a low, medium, or high profile heat sink, select the airflow from the
options of still air and airflow 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 (
SA
). The airflow should also be incorporated into
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 total
JA
, ambient temperature, and junction
temperature using
.
Figure 3–18
shows the thermal analysis, including the junction temperature (T
J
), total
JA
, and the maximum allowed T
A
values. For details on the values of the thermal
parameters not listed, click the Details button.
Equation 3–3. Total Power Calculation Using a Heat Sink
Figure 3–18. Thermal Analysis in the PowerPlay Early Power Estimator
P
TJ TA
–
JA
-----------------------
=