LTSpice op-amps

[CynicalMan]

I have LTSpice/SwitcherCad III, which has a very large database of op-amps.
My problem is that I usually want to simulate circuits using op-amps or power amps such as the TL0xx series, LM368, LM324, etc. All of the op-amps included in the program are LTxxxx. How can I find or make equivalents to the op-amps that I want to use?.

 

[Sceadwian]

You can specify the parameters of a basic op amp model to match the white sheet of your opamp. Spice models don't model the entire inner workings of an opamp, just it's functional equivilant. Fine tuneing of the opamp circuit should be done scoping the actual built circuit a simulation won't help with the real world details.

 

[audioguru]

There is a Yahoo website with many models of parts for SwCAD III.
Maybe somebody knows its address.

TheTL07x and TL08x opamps have the problem of Phase Inversion where the output suddenly becomes positive when an input becomes lower than the negative common mode range. Spice models might not know about it.

The lousy old LM324 and LM358 are very noisy, have a very low high frequency full output level and have crossover distortion. Spice models might not know.

 

[Sceadwian]

It's the Yahoo LTspice user group, just look it up under Yahoo groups. Far as I know all LTspice opamp models are behavioral based so the oddities of the actual silicon won't show up, good luck getting a 'true' spice model of an opamp. Using the basic opamp model and then testing the real circuit is really your best option, simulators just don't cover everything that come up, like component placement and odd parasitics that might be present. Look through the LTSpice help file and the generic opamp model, it will have a list of all the paramaters you can specify, with the white sheet for your opamp you can build a model for your opamp as good as you'll find anywhere else.

 

[audioguru]

I forgot.
Many high bandwidth opamps like the TL07x and TL08x oscillate at a high frequency when they try to drive the small capacitance of a shielded audio connection cable without having a 100 ohm resistor in series with the output.
A Sim program doesn't know anything about it.

 

[Sceadwian]

Well it could, but modeling all of the real world parasitics of any given setup is a nightmare, and you always forget, or don't know about something that will completely change the output. Shot/thermal noise alone make it impossible to practically simulate real world circuits, mainly at higher frequencies.

 

[Papabravo]

I always get the SPICE models from the manufacturers website. It's better than trying to do it yourself, especially if you know nothing about SPICE modeling. It's not a perfect solution, but I think it's ahead of whatever is in second place.

BTW you don really expect LTC to supply models for competitors "inferior and lower priced products" -- do you? You can find better opamps than LTC, but you won't pay more for them.

 

[Hero999]

Even testing won't filter out all the oddities as components differe extremely widely one TL082 might have a GBWP as much as twice as high as another.

The only way to fully test a produce is to mass produce it and tweak it during the production phase.

 

[Sceadwian]

Usually testing a few prototypes is a good idea first... How many product recalls could have been prevented with sanity testing? =)

 

[jvjtech]

I have LTSpice/SwitcherCad III [snip] How can I find or make equivalents to the op-amps that I want to use?.

Hi all, First post. I use LTspice and have found that the models and libraries available from Nat Semi, TI work with LTspice. At work, where we have Orcad Pspice, I have found that the Orcad libraries work in LTspice as these are "generic" and are supplied to Orcad (now part of Cadence) by the device manufaturers. Regards. jvjtech