LTspice IV can automatically create a symbol for a third-party model, or you can associate a third-party subcircuit with an LTspice intrinsic symbol, as long as the third-party .SUBCKT model and the intrinsic symbol share an identical pin/port netlist order. For example, to add an N-channel MOSFET transistor symbol to a schematic and define it with an IRF_7401 .SUBCKT statement:
- Add an instance of the N-channel MOSFET transistor symbol to your schematic.
- Move the cursor over the body of the MOSFET symbol and Ctrl + Right-Click. A dialog box appears.
- Change Prefix: “MN” to “X”. The symbol now netlists as a subcircuit instead of an intrinsic NMOS transistor.
- Change “NMOS” to be “IRF_7401”, corresponding to the name on the .SUBCKT line.
- Click OK.
- Either add the .SUBCKT IRF_7401 lines to your schematic or reference the library containing it (.INCLUDE third_party.lib) as a SPICE directive.
Again, this assumes the third-party model you’re adding follows popular pin order conventions. When in doubt, use the automatic symbol generation feature because it takes care of any discrepancies with regard to pin and port netlist order. For more about automatic symbol generation, see Help > Schematic Capture > Creating New Symbols > Automatic Symbol Generation.