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TINA/Spice/LM2904: TINA/Spice/LM2904 simulation result (design margin)

Hsu CD
Prodigy 160 points
Part Number: LM2904
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

• 30-degree phase margin is stable? But not in mass production.
• In above circuit, by adding a C1 220pF as capacitive load at the op amp output, there is a gain peaking about 7-dB meaning phase margin left about 20~30-degree.
• Could I say this circuit (single case) is stable?
• But considering mass production, there might be op amp internal compensation cap +/-20% variation in full temperature range and external component tolerance +/-20%.
  It is better to keep phase margin > 45-   degree as a rule of thumb.

  • Former Member
    0 Former Member in reply to Hsu CD
    Hello Hsu,

    Can you please try to reattach the image of your circuit?

    For some reason, we cannot see it on our side. Perhaps there was an issue in the attachment.

    Thanks,
    Daniel
  • 0 in reply to Former Member
    TI__Mastermind 30600 points
    Hi Hsu,

    As Daniel noted, if you could reattach your images, that would be helpful.

    A general comment on the current LM2904 model, it is quite inaccurate and old. We have a new model which will be available online in the next week or so.

    Addressing a few of your comments:

    * 30-degree phase margin is stable? But not in mass production.
    * It is better to keep phase margin > 45- degree as a rule of thumb.
    [TI] You are correct that 30 degrees of phase margin is not stable and that it is better to keep phase margin more than 45 degrees. To account for process, temperature, and variation, we actually prefer 60 degrees.

    * In above circuit, by adding a C1 220pF as capacitive load at the op amp output, there is a gain peaking about 7-dB meaning phase margin left about 20~30-degree. Could I say this circuit (single case) is stable?
    [TI] No, as you noted, we typically like more than 45 degrees for stability.

    Thanks,
    Paul
  • 0 in reply to Paul Goedeke
    Prodigy 160 points

    Hi, Paul and Daniel :

    Thankx so much for your kindly feedback.

    and let me re-attch the simulaiton result for your reference.

    If you have any further comments, just let me know.

    thankx again.

    CD

  • 0 in reply to Hsu CD
    TI__Mastermind 30600 points
    Thanks CD. No further comment from me, the new model will be released soon and it should be much more accurate as far as stability.

    If you have any other design questions, please let me know.

    Best,
    Paul
  • 0 in reply to Paul Goedeke
    TI__Genius 11800 points

    Hello Paul,

    Thank you for help!

    May I know roughly time frame that we can have revised LM2904 spice model?

    Thank you!

    Regards,

    Ting

  • 0 in reply to Ting Ye
    TI__Mastermind 30600 points

    Hi Ting,

    I'm hoping the new models will hit the web this week or next.

    Thanks,

    Paul

  • 0 in reply to Paul Goedeke
    TI__Genius 11800 points
    Hello Paul,

    Thank you for the great works!

    Regards,
    Ting