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PSS failing convergence on a SMPS model

I am working on a SMSP (switching mode power supply) model, by model I mean it is just made of analogLib, ahdlLib, and a custom Verilog-A elements.

Transient simulation shows it is stable and waveform also show periodic behavior. I am using the following Spectre version:

Version 18.1.0.169.isr2 64bit -- 12 Oct 2018

I use PSS Shooting to find the steady state. It comes close (I see convergence norms as low as 7) but fails convergence. It instructs me to reduce steadyratio which I set to 10e-3 (or 1e-2) but still fails.

It complains about signals who are perfectly behaving periodic with the beat frequency (there is only one tone).

Any idea what can be possibly wrong?

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fortune100worse over 6 years ago

I must also add that I see some unknown behavior from Spectre:

1) It seems to run tstab beyond the time I have set even though "Decide Automatically" is turned off. I asked it to run tstab for 15ms and it goes to 66ms!

2) It reports the following at the end of the log:

Maximum value achieved for any signal of each quantity:
V: V(I6.EA.cout) = 66.15 V
I: I(VINBAT:p) = 105.3 A
Initial condition solution time: CPU = 1.014 ms, elapsed = 1.01614 ms.

But both signals it reports don't show the values as high as it reports if you plot them!
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Andrew Beckett over 6 years ago in reply to fortune100worse

This is going to be pretty hard to debug without seeing it. You could have some instability in the models, or some variables that have non-periodic values. The maximum value issues can occur because the convergence might be diverging...

The best thing would be to contact customer support.

Andrew.
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Andrew Beckett over 6 years ago in reply to fortune100worse

This is going to be pretty hard to debug without seeing it. You could have some instability in the models, or some variables that have non-periodic values. The maximum value issues can occur because the convergence might be diverging...

The best thing would be to contact customer support.

Andrew.
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fortune100worse over 6 years ago in reply to Andrew Beckett

Hi Andrew,

Thanks for your feedback. I will file a Customer Support. If you don't mind, I will put you on CC.

Br,
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Slater over 5 years ago in reply to fortune100worse

Did you ever get this issue resolved with customer support? I am also having PSS convergence problems with a SMPS model.
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fortune100worse over 5 years ago in reply to Slater

Yes, it was solved. The issue had to do with Verilog-A models and their associated hidden states. Try to remove Verilog-A models and use components from analogLib to implement them. If problem persists, you may have to make your models more realistic (e.g. if you use switches to mimic a transistor, use some series resistors to model RDS). You should also remove all ahdlLib instances and figure out another way to model them using analogLib components.

Note: you can use also write Verilog-A models without hidden states but that can be tricky and difficult to figure out.
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Frank Wiedmann over 5 years ago in reply to fortune100worse

You can find more details about the hidden state limitation for Verilog-A models in Ken Kundert's paper "Hidden State in SpectreRF" at https://designers-guide.org/analysis/hidden-state.pdf
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