On Wed, Feb 26, 2025 at 11:07 AM, Robert wrote:
As it happens I'm struggling with this old SPICE chestnut right now, working on trying to model the effect of a PTC fuse.
This post resulted in me adding the directive:
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.OPTIONS ITL4=100 ABSTOL=1E-9 VNTOL=1E-3 RELTOL=0.01 CSHUNT=5e-12
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and that worked just fine for a while ... until I added an LT1375HV to the mix to try to move closer to what I actually want to model. ...
Did you try some or all of the options listed in the LTspice FAQ (Frequently Asked Questions) file?? Please see the message #
158795 that I sent earlier today about that.
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These "Timestep too small" errors do not have one remedy that always works.? That is why the FAQ file lists several things to try, and suggests trying all of them until you find something that works.
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More than likely, your original circuit already had issues which had prompted you to add those .OPTIONS to the simulation to get it to work - and they helped that one case.? Then, adding another component to the circuit changed the mix of part models that were in your simulation, causing the "time step too small" error to return.? Like I say, no single remedy always works.? You have to be persistent.
If it's any consolation, upgrading from LTspice XVII to the latest version after I added the LT1375HV didn't help me.
I would not expect that to make any difference.? It is not a bug in a version of LTspice.? Both versions have essentially the same simulator algorithms so they do pretty much the same thing.
Neither did switching to the Gear integration method, which was recommended in that post I referenced.
That is but one of several things to try.? Download and read that FAQ file, then start trying the many things it suggests to try.
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Tony's note about the rather large value for CSHUNT is important.? That number is "huge", and it is applied to every single circuit node!? It probably significantly (negatively) alters your simulated results, whether or not it helps avoid the "timestep too small" errors.? I think it should be at least one order of magnitude smaller than 5E-12.? The original note you said you got this from, did not mention CSHUNT, but it is one of the things that can help with these errors.
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Andy
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