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OPA379: Maximum open loop gain

Matt Crum
Prodigy 500 points
Part Number: OPA379

Hi. The data sheet for this device specifies the minimum open-loop voltage gain over temperature, but not the max.  Do you know what is the maximum open loop gain that can be expected?

  • 0
    TI__Guru* 93105 points
    Hi Matt,

    Certainly there is some practical limit to the open-loop gain (Aol) due to OPA379 design and process limits. There will be a normal distribution for Aol, just as there are for most op amp electrical parameters.

    I don't have data for the OPA379 maximum Aol because that isn't usually the concern, but I would expect the delta from the "typical" for the maximum to be about the same minimum, or 10 dB. That would put the maximum at about 130 dB. That would be the equivalent of about 3.2e6 V/V max, vs 1e6 V/V typical.

    Regards, Thomas
    Precision Amplifiers Applications Engineering
  • 0 in reply to Thomas Kuehl
    TI__Prodigy 500 points
    Thomas,

    Follow up question -

    Thanks for your response. The problem I'm looking at is one of stability. Trying to assess if we are at risk in our circuit using the OPA379, I ran an AC analysis in simulation to get the open loop phase and gain margins. When I do this with the OPA379 model from the TI web site, the result says the circuit has 53 degrees phase margin and 13 dB gain margin. I checked the performance of the model and found that the gain it has matches the typical gain from the datasheet. Then I put a gain-of-ten block in the loop and simulated again. The result indicate an unstable circuit.

    Two things I'm uncertain about : is a gain of 10 inconceivable (your reply says that it is conceivable); and in an opamp, if the gain varies from unit to unit, will the corner (-3 dB point) of the gain rolloff versus frequency change with the change in gain. Along with that, would the corner change to a lower frequency with increasing gain? Does the gain bandwidth product increase if the gain increases?

    -Matt
  • 0 in reply to Matt Crum
    TI__Guru* 93105 points
    Hi Matt,

    Can you please provide us the schematic for the OPA379 circuit you are evaluating?

    Regards, Thomas
    Precision Amplifiers Applications Engineering