This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

OPA567: Performance with large load capacitance

Part Number: OPA567

Hi,

Im planning on using the OPA567 in a battery simulator circuit. One concern I had is how the circuit behaves with large load capacitances (1mF bulk cap). I simulated it in TINA and the stability looked okay (1ohm Riso), but wanted to make sure the model is okay as the overshoot vs load capacitance graph shows ~50% overshoot at 10nF.

Thanks!

  • Hi,

    Can you send us your OPA567 TINA circuit file so that we can see exactly what you are planning? There's a reasonable chance that the OPA567 will be stable driving the 1 mF load when you include the Riso of 1 Ohm, and the capacitor's equivalent series resistance (ESR). Do realize that adding such a large capacitance at an op amp's output kills the bandwidth, but that isn't usually an issue in high C-load applications.

    The model should be pretty close. Once we have the information I can check the stability.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • Thanks Thomas,

    Sorry, I guess the picture didnt get attached on my last post. Hopefully the schematic gets attached this time. The much lower bandwidth shouldnt be a problem for my application. 

    Thanks,

    Josh

    opa567.TSC

  • Hi Josh,

    The your enclosed circuit will be stable to drive 1mf capacitor with Riso of 1Ohm in series with a battery load. However, the circuit will not work for testing a battery. 

    The battery's internal impedance is very low, and it is likely in an order of mOhm to x*100th mOhm (depending on the types and size of batteries). It looks like you are testing 3.3V battery, and most of voltage will be dropped across the Riso in the circuit when charging. The Riso has to be placed inside of OPA567's feedback loop, and likely the circuit has to use dual compensation methods to stabilize the OPA567 driver (BTW, will require to compensate the circuit again, if Riso is placed inside of feedback loop.). 

    What is the OPA567's BW for your application?

    Best,

    Raymond 

  • Hi Josh,

    yes, your circuit looks stable. There's enough phase margin:

    josh_opa567.TSC

    Raymond, I don't think that Josh is testing batteries with this circuit. I think the circuit shall simulate a battery :-)

    Kai

  • The circuit is stable with 88 degrees phase margin - see below.

  • Thank you all for the quick replies!