Airflow, Airflow -2 – Altera PowerPlay Early Power Estimator User Manual
Page 54
If the HDL is complete, the best way to determine toggle rate is to simulate the design. The accuracy of
toggle rate estimates depends on the accuracy of the input vectors. Therefore, determining whether or not
the simulation coverage is high gives you a good estimate of how accurate the toggle rate information is.
The Quartus II software can determine toggle rates of each resource used in the design if you provide
information from simulation tools. Designs can be simulated in many different tools and the information
provided to the Quartus II software through a Signal Activity File (
.saf
). The Quartus II PowerPlay Power
Analyzer provides the most accurate power estimate. You can import the Comma-separated Value file
(
.csv
) from the Quartus II software into the PowerPlay EPE spreadsheet for estimating power after your
design is complete.
Airflow
It is often difficult to place the device adjacent to the fan providing the airflow. The path of the airflow
might traverse a length on the board before reaching the device, thus diminishing the actual airflow the
device receives. The following figure shows a fan that is placed at the end of the board. The airflow at the
FPGA is weaker than the airflow at the fan.
Figure 4-2: Airflow and FPGA Position
FAN
FPGA
You must also consider blocked airflow. The following figure shows a device blocking the airflow from the
FPGA, significantly reducing the airflow seen at the FPGA. The airflow from the fan also has to cool
board components and other devices before reaching the FPGA.
Figure 4-3: Airflow with Component and FPGA Positions
FAN
FPGA
Device
If you are using a custom heat sink, you do not need to enter the airflow directly into the PowerPlay EPE
spreadsheet but it is required to enter the θ
SA
value for the heat sink with the knowledge of what the
airflow is at the device. Most heat sinks have fins located above the heat sink to facilitate airflow. The
following figure shows the FPGA with a heat sink.
4-2
Airflow
UG-01070
2015.01.20
Altera Corporation
Factors Affecting the PowerPlay Early Power Estimator Spreadsheet Accuracy