Importing models into LTSpice, time step too small error

Discussion in 'General Electronics Chat' started by IsoPhaseCore, Oct 24, 2011.

  1. IsoPhaseCore

    IsoPhaseCore Thread Starter New Member

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    I am trying to import a new model, an AD633 multiplier, and have created a new symbol for it. However, I am getting a 'time step too small' type of error. I've tried increasing the Trtol value (as SgtWookie suggested in an older thread) bringing it up to over 20, but still have the same flavor of error.

    Any suggestions? I've attached the model, symbol (had to zip these to get them to attach) and circuit files.

    Thank you for your help!

    Attached Files:

  2. chrisw1990

    chrisw1990 Active Member

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    i had a problem like this yesterday, it was simply that the circuit stopped working.. crashed if you like.. very odd
  3. IsoPhaseCore

    IsoPhaseCore Thread Starter New Member

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    I've got it! I followed the advice in this thread:
    http://forum.allaboutcircuits.com/showthread.php?t=60825

    and I was able to get it to work, now I just need to adjust my variable input voltage and current readings (slower time is needed I'm guessing?) to see how the IC reacts.
  4. IsoPhaseCore

    IsoPhaseCore Thread Starter New Member

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    I'm attaching the files for the 'working' version. However, the simulation is very sensitive to the input values I enter. I'd appreciate if anyone could advise on what Spice settings I could change to help stabilize it (so that I can vary the input in 1 us time frames and test the slew rate / bandwidth of the IC in the model).

    Thanks!

    Attached Files:

  5. SgtWookie

    SgtWookie Expert

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    I tried grounding all the inputs (X1, X2, Y1, Y2 and Z), leaving only W connected to ground via a 1k resistor; timestep error.

    The only way I could get it to complete running was to leave X1 and Y1 open.

    There's something strange going on with that model.

    I looked in the Yahoo! LTSpice user group, and found this exchange:

    I tried the Alternate solver, and only positive inputs - then only negative inputs. Didn't help.

    Another:

    I'd tried the different solvers, tried the statements, nothing seems to work except to leave the inputs floating.

    Instead of a transient analysis, try a DC analysis.
  6. SgtWookie

    SgtWookie Expert

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    I didn't see your reply before I posted mine.

    Don't bother trying to test the slew rate for this, as it's a macromodel, not a component model. You'll have to go by the specifications in the datasheet.
  7. IsoPhaseCore

    IsoPhaseCore Thread Starter New Member

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    Hey Sgt, I tried the alternate solver (along with my latest sim settings, and slower input values in posts #2 & 3) and it did help to stabilize the simulation more. It's not perfect, but no model is, and I think it is good enough. Thanks for your help!
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