Altera PowerPlay Early Power Estimator - Manual (Page 39)

Chapter 3: Using Cyclone III PowerPlay Early Power Estimator 3–27
Factors Affecting PowerPlay Early Power Estimator Accuracy
© June 2009 Altera Corporation PowerPlay Early Power Estimator User Guide for Cyclone III FPGAs
When placing the heat sink on the FPGA, the direction of the fins must correspond
with the direction of the airflow. The top view shows the correct orientation of the fins
(
Figure 3–24 ).
These considerations can heavily influence the airflow seen at the device. When
entering information into the PowerPlay Early Power Estimator, you must consider
these implications in order to get an accurate airflow value. You must determine the
actual airflow at the FPGA and correctly input this value into the PowerPlay Early
Power Estimator.
Temperature
The PowerPlay Early Power Estimator requires you to enter the ambient air
temperature for the device in order to calculate the thermal information of device
correctly. Ambient temperature refers to the temperature of the air around the device.
This is almost always much higher than the ambient temperature outside of the
system. To get an accurate representation of ambient temperature for the device, the
temperature must be measured as close to the device as possible. This can be done
with a thermocouple.
Entering an incorrect ambient air temperature can drastically alter the power
estimates in the PowerPlay Early Power Estimator.
Figure 3–25 illustrates a simple system with the FPGA housed in a box. In this case,
the temperature is very different at each of the numbered locations.
Figure 3–24. Heat Sink (Top View)
F
A
N Heat Sink Fins
Figure 3–25. Temperature Variances
F
A
N
1
2
3
4
FPGA