On Thu, 20 Mar 2014 12:01:35 -0400, Phil Hobbs
wrote:

[snip]

A lot of TI's op amp models don't play at all well in LTspice--try the
OPA140, for instance. None of the tricks on the webpage below help that
one at all, whereas it converges instantly with an LM358 macromodel (fwiw).

Easy to see why...

..MODEL S_VSWITCH_1 VSWITCH (RON=1 ROFF=100MEG VON=100M VOFF=-100M)
..MODEL S_VSWITCH_2 VSWITCH (RON=1 ROFF=100MEG VON=100M VOFF=-100M)
..MODEL S_VSWITCH_3 VSWITCH (RON=1 ROFF=10MEG VON=100M VOFF=-100M)
..MODEL S_VSWITCH_4 VSWITCH (RON=1 ROFF=10MEG VON=100M VOFF=-100M)
..MODEL S_VSWITCH_5 VSWITCH (RON=10M ROFF=100MEG VON=150 VOFF=0)
..MODEL S_VSWITCH_6 VSWITCH (RON=10M ROFF=100MEG VON=150 VOFF=0)
..MODEL S_VSWITCH_7 VSWITCH (RON=1M ROFF=10MEG VON=-10M VOFF=0)
..MODEL S_VSWITCH_8 VSWITCH (RON=1M ROFF=10MEG VON=10M VOFF=0)
..MODEL S_VSWITCH_9 VSWITCH (RON=1 ROFF=10MEG VON=1 VOFF=-1)
..MODEL S_VSWITCH_10 VSWITCH (RON=1 ROFF=10MEG VON=1 VOFF=-1)
..MODEL S_VSWITCH_11 VSWITCH (RON=1 ROFF=1G VON=10 VOFF=-10)
..MODEL S_VSWITCH_12 VSWITCH (RON=1 ROFF=1G VON=10 VOFF=-10)
..MODEL S_VSWITCH_13 VSWITCH (RON=1 ROFF=1G VON=10 VOFF=-10)
..MODEL S_VSWITCH_14 VSWITCH (RON=1 ROFF=1G VON=10 VOFF=-10)

Whoever writes TI's models doesn't know how to apply bounding
conditions except with a switch.... all those switches cause static
convergence problems.

You could substitute Mike's TANH-based switch and see if that helps.

Of course the model works quite well in PSpice in spite of those
switches :-}



There's a list of convergence suggestions at http://tinyurl.com/ox4fkfe
. It points out that the source stepping mode uses short time steps in
order to make the capacitances dominate the impedance, so that
everything starts up smoothly from zero.

You can set a minimum capacitance from each node to ground

.options cshunt=10f

Cheers

Phil Hobbs

Often what works around all these obstacles is to have your power
supply be a pulse- or PWL-based source... start up from zero (in a
..TRAN situation) seems to work every time.

...Jim Thompson
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