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OPA211 open loop behaviour - TINA

Bart van der Laan1
Prodigy 10 points

Other Parts Discussed in Thread: OPA211

Hello,

I'm using the OPA211 TINA model to simulate a circuit. When I wanted to check that circuit's phase margin, I came across some weird behaviour of the OPA211 model. The model does not provide a correct Open loop behaviour, as do other models like the OPA140. On the other hand, an OPA134 model does provide an expected result. Does anyone know what causes this? I want to be sure the model is correct before continuing to use it.

Best regards,

Bart

  • 0
    TI__Mastermind 40295 points

    Bart,

    Unfortunately I was unable to reproduce your results with a conventional circuit configuration.
    So I tried using a more idealized circuit to correlate the model's open-loop behavior with the curves published in the data sheet.
    To that end, the attached TINA circuit provides an OPA211 open-loop response.

    It was created from the reference design available in the device product folder: http://www.ti.com/product/opa211#simulationmodels
    or from the complete list of TINA models and reference designs: http://www.ti.com/spicerack
    Using the reference design as a starting point, the feedback was removed and an 30.38uV DC offset was added to the signal source to compensate for the input offset.
    This results in a residual offset of 200uV at the device output, which is close enough to mid-rail to serve our purpose.

    The major difference between the modeland the data sheet appears to be at low frequencies.
    The amplitude roll-off in the data sheet plot appears to be at about 300Hz, while the model's is about 20Hz.

    The typical DC gain in the data sheet is the same as the model, 130dB.

    The model's unity-gain crossover point is 38.71MHz, and the model's phase margin at this frequency is 61.2 degrees.
    This seems to agree with the data sheet plot.

    Hope this helps.
    If it doesn't, and you are still not getting the results you want, would it be possible to upload your circuit to this thread?
    That would be the easiest way to see what's going on and to help resolve the problem.

    Regards,
    John

    OPA211_OpenLoopGain.TSC