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LM837 PSpice Model Experiencing Convergence Problems

Michael Arriete56
Expert 3295 points
Other Parts Discussed in Thread: LM837

Team,

We're modeling a section of a new design using the LM837. After downloading the PSpice model from the TI web page, we saw convergence problems. The design is powering the op amp with +12 and -15 voltage sources. If we balance the sources (+/-15 or +/-12) the model works fine. Is this a model issue or should we expect problems powering the amplifier from unbalanced sources?

Best regards,
Michael Arriete

  • 0
    TI__Guru* 95145 points
    Hi Michael,

    LM837 datasheet does not mention operation in unbalanced source situation. So I think this is not really recommended and also the performance may not be as shown in the datasheet.
    I think webench model is working different than the PSpice model.
    Besides, using unbalanced sources will affect the output center voltage reference and may reduce the dynamic range.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Prodigy 110 points

    Hi Ivan -

    Thank you for the response. A couple follow up questions:

    1. Does TI make an amplifier that is rated for use with unbalanced bias?

    2. You mentioned that the web bench model was different, does that mean that the web bench model operated normally with unbalanced bias?

    3. Can you suggest conditions that would be more likely to show problems (e.g.high / low temperature or exaggerating the unbalance)? 

    Best regards

    - Bill

  • 0 in reply to Bill Baker1
    TI__Mastermind 49896 points

    Hi Bill,

    The LM837 should not have an issue with "unbalanced" supplies (the correct term is "asymmetrical" supplies).

    I have seen it work happily with single supplies (0 and +12) and other "asymmetrical" supplies. As long as it has a minimum of about 6V across the supplies - it should be happy. Most likely this is a model issue.

    However, the LM837 is not a R-R input device, so the voltages on the inputs need to be 1V away from either rail (+11 to -14 for you). The model header states that it does model the common mode range. The model may be choking on this if it is trying to simulate a common mode violation - say if the inputs are less than a volt from the rail.

    So it looks like a case of the model not matching the real-world device.

    You can post over on the Webench support forum to get help with troubleshooting the model.

     http://e2e.ti.com/support/development_tools/webench_design_center/f/234

    Regards,