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OPA392: About open-loop output impedance

diverger
Expert 1510 points

Part Number: OPA392

It seems the simulated open-loop impedance different from the datasheet significantly at low frequency.

image.png

  • 0
    TI__Guru 72991 points

    If you use a logarithmic vertical scale instead of linear and limit the frequency range to 1Hz to 10MHz shown in the datasheet, you will find the graphs closely match. The only discrepancy between the graphs is at low frequency (between 1Hz and 10Hz), which has to do with the magnitude of the AOL.  This is not important from the stability point of view, which is determined at much higher frequency where AOL and invBeta intersect.

  • 0 in reply to Marek Lis
    Expert 1510 points

    So, which one is right? The sim model or the datasheet?

  • +1 in reply to diverger
    TI__Guru 72991 points

    The Zo simulation model and graph are not much different - see below.  Besides, they are TYPICAL performance specifications and thus the actual Zo would vary dependent on DC open-loop gain (AOL).