Common Errors - Unmodeled Parts or Pins

Once you start doing actual designs, a common problem occurs because of parts and pins that are not modeled.  The greatest problem with these errors, is that they are often not 'fatal' errors, but result only in DRC warnings on the schematic.  The simulation may process apparently normally, with the only indication of problems showing up in bogus simulation results.

Unmodeled Parts
The most common cause in using parts that do not have an underlying simulation model, is the use of parts found in the standard Orcad libraries that are NOT in the PSpice subdirectory.  There are several directories of libraries that are included in Capture for use in PCB Layout, schematic design, or FPGA design, that are not usable in a PSpice design. If you have placed one of thes parts from these libraries, then you will need to delete it, and either find or create a new part that has an associated model.

Indicators of PSpice parts
When you go to place a part in Capture, take a look at the bottom of the dialog box.  When you select a part with a PSpice model associated, or a PCB footprint, you will see a little icon for PSpice or Layout along the bottom.  Unfortunately, most of us never look at these icons...

Model Not Found
Another common error is Model Not Found for part XXXX.  This is especially common when you are creating parts from a simulation library you have downloaded, or have made yourself.  This means that either a.) you forgot to configure the library that contains the model or b.) you have misspelled the name of the model in the part.

To add a model library to your configuration, you need to open the simulation profile.  There you will see a Configuration Files tab.  Click on this, and select the Library category to get a list of the presently configured model libraries.  The first one you should see if nom.lib.  This is a file that contains a list of all the standard configured libraries that came with your version of PSpice. Do not edit this file, as it gets updated every time you do an installation and may get changed during an update.  Always add your files separately from nom.lib.

To add your own model libraries, hit the browse button and find your model library, and click add.  In the Configuration Files dialog, select one of the Add buttons.  Each one has a different scope.  Add to Profile means that this library will only be used by this simulation profile, useful for simulating corners or other specific use models.  Add to Design means this library will only be available for this design.  If you create a new design, these models will not be seen.  Finally, Add to Global adds this model library to the list of libraries available to all your designs.

Unmodeled Pins
When you have Unmodeled Pin DRC warnings, they can have two causes.  First, the part itself has no model, so the pins have model nodes attached. That we covered above.  Sometimes, however, the pins have been left unmodeled intentionally. One common cases for this are the CLOCK pins on some of the PWM switching regulators.  Instead of using an attached RC to determine the clock, the model has an internal parameter set from the Properties Editor to set the frequency, Some OPAMP symbols also have unmodeled compensation pins, where the compensation is set internal to the part, or is not modeled at all.