I agree, of course, but the AD797 is a
(costly) opamp. It should not produce a TSTS error in that .ASC.
Without a lot of digging, it isn't possible to confirm that it
is connected correctly; for example, is node 38 really the
output? The .ASC appears to work with the simple opamp.. It
could hardly refuse.
On 2025-02-24 14:52, Andy I via
groups.io wrote:
On Mon, Feb 24, 2025 at 09:03 AM, john23 wrote:
Hello ,I have the following file which is presenting an
error shown below
...
Convergence Failure: ?Time step too small; time =
8.11724e-08, timestep = 1.25e-19: trouble with instance
"u1:DSC1"
I assume this is the failure you asked about.
?
"Time step too small" errors are unfortunately difficult to
deal with.? If this is your first time encountering a "timestep
too small" error, "welcome to the club".
?
"Time step too small" errors happen for this reason.? When
SPICE can't converge at any timepoint, it backs up to the
previous one, sets the time step smaller (I think by a factor of
8), and tries again.? It is more likely to find convergence by
not trying to go too far into the future, so a smaller timestep
after the last good point is more likely to solve, and then it
can move on.
?
But occasionally that doesn't work.? It keeps trying smaller
and smaller timesteps, until eventually the timestep gets
ridiculously small, and SPICE/LTspice aborts with that error
message.
?
The root problem is most likely because there is something in the
circuit that behaves badly.? Maybe a component's function or its
derivative has a discontinuity.? Both are bad for SPICE and
should never happen, but many models have discontinuities and
can lead to these problems.? The best remedy is to fix the
models.? But often we can't do that.? There are a handful of
other things that can sometimes help,?
?
Download the
FAQ file.?
Open it and read until you find the section about "time step too
small" errors, and start reading.? There are a couple dozen
suggestions that MIGHT help.? There is no guarantee that you can
ever fix a "time step too small" error.
?
When I ran your simulation, I do not (yet) have a "time step
too small" error, but it has not found the initial DC solution
yet.? Time step too small errors can happen even during the
initial DC solution phase, because one of the algorithms is
"Pseudo-Tran", which applies the transient solver to finding the
DC solution.? Sometimes it can abort in that phase, even though
it is not a .TRAN simulation at all.
?
Andy
?
?
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
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John Woodgate