LTSpice V

fonik

hi all,

i am currently working with a very old edu version of electronic workbench. easy to use but one cannot import 3rd party models and i do missing OTA's.

i just downloaded LTSpice V and tried to import nationals LM13700 spice model, following the instructions of the LTSpice manual - without success. obviously i cannot establish a correct connection of symbol and model. i must be doing something wrong with the symbols attributes?

what i did so far:
i drew a symbol and placed pins, using the numbers from the lm13700.mod file.
i then renamed the lm13700.mod file to lm13700.lib and moved it into the 'sub' subdirectory.
i edited the symbols attributes:
Symbol type: Cell
Prefix: x
SpiceModel: lm13700.lib
Description: LM13700 OTA
i left all other fields empty

when i place the component to an empty schematic and run the simulation i get following error message:

Oli · Posted: Wed Jun 17, 2009 12:51 am Post subject:

Hi,

I'm having the same problem using LTSPiceIV. I think LTSpice likes to have subcircuits defined in a .sub file, rather than a .lib, and add a SPICE directive manually .include *.sub .

I'm still coming to terms with the details of this though.

I think the manual is a bit inadequate/misleading. I think many users have had the same issue.

There is a Yahoo! group for LTSpice users. I think I'll join up there, as I am finding the program useful for simulating SMPSs. It gave me some interesting results which I wouldn't have guessed from reading data sheets. I'm yet to confirm the results in test.

Cheers,

Oli

fonik · Posted: Wed Jun 17, 2009 1:04 am Post subject:

thanks for the reply. BTW i solved it!

you have to copy your model and symbol file into the same directory as your schematic (i.e. 'Projects') and specify the path in the component you created.

then you have to add a command line to the schematic with the include argument.

this is described in detail in the LTSpice yahoo group.

bearblock · Joined: Sep 27, 2006 Posts: 90 Location: uk Audio files: 1

hi - thought i'd resurrect this thread instead of making a new one since my query is pretty closely related.

i'm working on a new circuit that will probably end up using LM13700s, so i've imported the model into LTSpice as detailed above. to test it out i built simulations of a couple of circuits from the LM13700 datasheet (unity gain follower and voltage-controlled low pass filter) which both seemed to work ok.

i've run into a brick wall using the simulated LM13700 as a voltage-controlled integrator though. my circuit works fine with basic RC opamp integrators, but when i substitute LM13700 VC integrators, the outputs run into the rails almost straight away, and stay there.

since Ian Fritz's Jerkster uses the chip in the same way as i'm trying to, i thought i'd build it in LTSpice and see what happens; again, the output runs into the rails. i have a Jerkster in my modular so I know it works in real life; i don't really understand why the simulation fails?

can anyone spot any stupid errors i may have made in the attached screenshot? or alternatively: can anyone educate me about possible inaccuracies in the Spice model which might cause this kind of problem? i don't think it's a chaos thing, as i've got Chua's oscillator etc. working in LTSpice.

if no one can think of anything i'll probably just continue development on breadboard, but it would be really good to shed somelight on this. can provide more info if it will help.

thanks for reading!

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