Well after a day of fiddling about with the values in my .OPTIONS and different integration methods (including the suggestions in the FAQ), I finally got my circuit modelling with just:
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.OPTIONS ITL4=100 ABSTOL=1E-9 VNTOL=1E-3 RELTOL=0.01
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You'll notice I took out CSHUNT. 5e-12 was the value I had to use (with LTSpice XVII) before I added the LT1375HV. Now I have got the model to converge with the LT1375HV (for the moment, at least; I have more things I need to add), I found that I could make CSHUNT anything from 5e-20 to 5e-12, with no obvious effect, so I then removed CSHUNT completely and it still converges. So what did I do to make it converge?
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What I'm trying to determine is inrush current, so I have a PWL voltage source set to mirror what the external power supply will do when the test is performed for real. I happened to have it going from 0 volts at 1 ms to 28 V at 2 ms (because the test is defined in ms, and I like to steer clear of whatever SPICE does at time 0). Sometimes it's good to leave a problem overnight, and in the middle of the night I realised the model always fell apart before it got to 1 ms.? ?So this morning I simply changed the voltage generator to go from 0 at 1 ?s to 28 V at 1 ms, and the problem went away >doh!<. I do still need the .OPTIONS line above, but I'm using the default integration method (which is trapezoidal on LTSpice 24).
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So there's another way to address the problem; timeshift the model so the circuit is doing something different at the time when the non-convergence kicks off.
