Using Microchip's op amp SPICE macro models
The SPICE macro models for Microchip’s operational amplifiers (op amps) aid in the design and analysis of various circuits by allowing for detailed simulation of the circuit being designed. This app note does not explain how to use the circuit simulator but will give the user a better understanding how the model behaves and tips on convergence issues.
Microchip’s op amp SPICE macro models cover a wide aspect of the op amp’s electrical specifications. Not only do the models cover voltage, current, and resistance of the op amp, but it also covers the temperature and noise effects on the behavior of the op amp.
Microchip’s op amp SPICE macro models were written and tested in Orcad's PSPICE 10.0 which is equivalent to Cadence PSPICE 15.x. The type of modeling technique that was used to model the op amps is called "Macro Modeling". It is based on treating the op amp as a black box and using mathematical equivalents of the internal functions. As opposed to macro modeling, transistor level modeling is used for modeling of the device under development and fabrication.
Microchip’s op amp SPICE macro models are provided in netlist format. This is useful for simulating the models in a number of different simulators. Please refer to your simulator software reference manual on how to create a schematic symbol and relating a netlist to the symbol. All SPICE simulation schematic tools are different in their creation of a schematic symbol and relating it to the library file.
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SPICE free version
Being included in the SPICE device library is always a welcome development especially for designers. But do you know that there is a free (student) version of SPICE? You can check on CircuitLogix, which is a SPICE-based simulation package. This is the same product as the full version of CircuitLogix with the following limitations:
- 2D simulation only
- Maximum of 50 devices per design
- Device library limited to 1,000 models
- Symbol editor and Macro feature disabled
RE: SPICE free version
One of the best available versions of FREE spice is LTspiceIV supported by LinearTechnologies. A series of articles on this subject will be coming up soon here, on EMCelettronica, detailing various types of simulations. The best thing about LTspiceIV is that it is free and COMPLETE, i.e. there are no limitations with respect to the number of nodes you devices. It comes with a pretty good library et (containing mostly LT parts, of course, but you can add your own models, and one of the tutorials presented here will describe exactly how to do this).
Regards,
Cristian
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