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OPA192: Loop gain simulation

Kuramochi Tadahiko
Guru 28715 points
Part Number: OPA192
Other Parts Discussed in Thread: TINA-TI,

Hi,

I would like to simulate the stability with each temperature on TINA-TI.

Simulating the stability, I need inputting the equivalent to calculate loop gain as below.

However, the error message appears when I executed with temperature stepping.

Could you tell me how to simulate stability with temperature stepping without error?

Best Regards,

Kuramochi

   

  • 0
    Guru 48395 points

    Morning Kuramochi,

    Aside from your TINA question, keep in mind the critical model elements (dominant pole in the Aol, higher frequency poles, open loop output impedance) do not have tempco coefficients in the model. 

  • 0
    TI__Guru* 93105 points

    Tadahiko-san,

    The op amp simulation model that the OPA192 model uses is a behavior model. It does not use transistors to provide the equivalent performance and behavior of the op amp, but instead relies on controlled sources and mathematical models to emulate them. The model is very complex and does not include temperature coefficient and responses as Michael indicated. The OPA192 open-loop gain (Aol) changes little temperature as can be seen in the datasheet Figure 30, Open-Loop Gain vs Temperature so any change in ac behavior related to Aol should be minimal.

    If the circuit you are running the stability analysis produces a particular phase margin at 25 C, changing the temperature in the real OPA192 circuit shouldn't affect the phase margin by more than a few degrees. We run stability analyses on customer circuits often using the nominal 27 C Pspice temperature, and if a good phase margin is obtain (>= 45 degrees) it isn't going to move far enough for the stability to be compromised. 

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Guru 28715 points

    Hi Thomas-san,

    I understand.

    Does it mean that we cannot simulate the stability with each temperature on TINA-TI?

    Best Regards,

    Kuramochi

  • 0 in reply to Kuramochi Tadahiko
    TI__Guru* 93105 points

    Hello Kuramochi,

    Yes, the model does not provide the ability to simulate the circuit stability at different temperatures.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Guru 28715 points

    Hi Thomas-san,

    My customer has an additional request.

    Could you provide the worst parameter(for stability) model of OPA192?

    Best Regards,
    Kuramochi

  • 0 in reply to Kuramochi Tadahiko
    TI__Guru* 93105 points

    Kuramochi,

    The stability behavior of the OPA192, or any op amp, is a function of the open-loop gain (Aol) and phase vs frequency (Bode response), the complex open-loop output impedance (Zo) vs frequency, and the actual circuit in which the op amp is placed. When we design and construct the op amp simulation model the Aol and Zo vs frequency characteristics are carefully incorporated in the model. Therefore, when it is applied in a simulation circuit with the intended components around it, the true closed-loop behavior should be observed by the simulation. The results for our TI op amps using our newer behavioral op amp model should provide accurate ac results. Note that some of our competitor's models do not include the level of ac sophistication that we do in our TI op amps models.

    It is best not to alter the op amp model for a "worst" parameter because the behaviors are interdependent. If you have a specific OPA192 circuit that you need help running a stability analysis we can assist.

    Regards, Thomas

    Precision Amplifiers Applications Engineering