3.2 Set up a POP Analysis
In this section, you will set up a SIMPLIS
Periodic Operating Point (POP) analysis which finds the
steady-state operating point of the converter.
This topic addresses the following key concepts:
- In order for the POP analysis to find the steady-state operating point it needs to
know which node on the schematic represents the lowest periodic frequency. You
identify the lowest periodic frequency node with a special SIMPLIS symbol, the POP
Trigger Schematic Device.
- The POP trigger model is unique to SIMPLIS and contains a reference voltage and
- The POP trigger device tells SIMPLIS which node to use to detect the beginning of
each new POP period during the Periodic Operating Point analysis.
- This schematic node should trigger the POP trigger to switch at the lowest frequency
at which the entire system is periodic; in other words, the lowest frequency at which
every energy-storage element in the system exhibits periodic behavior. For this
converter, any voltage which switches at the 500kHz switching frequency can be used
for the POP Trigger input.
What You Will Learn
In this topic, you will learn the following:
- How to add a POP trigger to the schematic
3.2.1 Add a POP Trigger to the Schematic
To add a POP trigger,
follow these steps:
- Open the schematic that you saved after running the transient simulation
- From the Part Selector, double click on the Commonly Used Parts category to
expand the list.
- In the expanded list, double click Pop Trigger Schematic Device.
- Place the cross hair directly above the inductor, and click the left mouse button to
place the POP trigger.
Note: If you need to move the POP Trigger symbol after you
place it, press and hold the left mouse button on the symbol and then drag the
symbol lower on the schematic.
To use the switching node as the periodic source, follow these steps to connect the
- Make sure that the trigger is deselected, and place the cursor at the end of the
line on the left side of the POP trigger.
cursor changes from a cross hair to a pencil.
- Click the left mouse button, and draw a short horizontal line to the left.
- Click the left mouse button again to create a corner, and extend the wire to the
line that connects to the voltage probe for the switching node.
- Click the left mouse button again to make the connection and then click the right
mouse button to finish the wire.
should now look like this:
- To save this version of the schematic, select
from the menu bar in the schematic editor.
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3.2.2 Set up the POP Analysis
To set up the POP analysis directives, follow these steps:
- From the menu bar in the Schematic editor, select
Result: The Choose SIMPLIS Analysis
- Click the Periodic Operating Point tab.
- In the Select analysis section on the upper right side of the dialog box,
check POP and uncheck Transient.
- To specify the maximum switching period for your circuit, go to the Timing
section of the dialog and change the Maximum period value to 2.2μs.
Note: This Maximum period value is 110% of your steady-state period. The maximum
period parameter limits the solution space in which POP searches for a steady
state condition. The maximum period parameter must be greater than the switching
period but it is recommended that it not be set to more than two times the
- After you enter the analysis directive parameters, do one of the following:
- Click the Run button.
- Click Ok to save the data and press F9 to run the
Result: The waveform viewer window opens with the
steady-state waveforms for your converter.
In the window shown above, the probed
waveforms for VOUT, SW, and IL are displayed for five periodic switching cycles. Notice
that the converter displays no settling behavior and the waveforms are in perfect
steady-state. The POP algorithm can save enormous amounts of elapsed time by
accelerating the simulation to the correct steady-state operating
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3.2.3 Save your Schematic
To save your schematic, follow these steps:
- Navigate to your working directory where you are saving your schematics.
- Name the file 4_my_buck_converter.sxsch.
A schematic saved at this state can be downloaded here:
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