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TPS53681: about TPS53681 frequency response analyser 0-dB frequency

user6304695
Prodigy 110 points
Part Number: TPS53681

Hi

      I use TPS53681+3*CSD95490 supply power 0.9V/100A，Fsw=500KHz，test loop stability，find 0-dB frequency (f0=155KHz) is too high，

I'm trying to debug AC_GAIN to decrease and AC_LL to increase it worked.

so，How do you recommend debugging？

shaocong

thanks

  • 0
    TI__Genius 11095 points

    Hello,

    TPS53681 is a variable frequency controller - pulse frequency increases as the loop is perturbed. It is not necessarily a major risk to have Fco > 20% * Fsw. You can reduce the crossover frequency, as you suggested by reducing the AC Gain and ACLL values in the compensator. Integration gain and time constant are mostly low frequency effects. You may also want to try measuring Vout from the local catch resistors in the voltage feedback, instead of the remote point to see the result.

  • 0 in reply to Matt Schurmann
    Prodigy 110 points

    Hi Matt

       What are the judgment conditions for the stability of the power loop corresponding to the frequency conversion controller？

    thanks

  • 0 in reply to user6304695
    TI__Genius 11095 points

    Hello, Monday is a US holiday and we’ll reply by tomorrow EOB 

  • 0 in reply to Matt Schurmann
    TI__Genius 11095 points

    Hello, Usually we look for 45 degrees phase margin, >6dB gain margin, and look at the time domain transient response and jitter to judge the stability. As long as these things are maintained, I would not be concerned about the Fco being higher than a comparable fixed frequency controller.

  • 0 in reply to Matt Schurmann
    Prodigy 110 points

    Hi,Matt：

        I have a few more questions to consult you？

    1、For example，if 45 degrees phase margin have two point(or more point) in the loop ，we should choose which one？

    2、you say time domain transient response meaning of dynamic response？

    3、What do you mean about jitter？phase jitter？

    Thanks

    shaocong

  • 0 in reply to user6304695
    TI__Genius 11095 points

    Hi Shaocong,

    1- I think you mean if there is a double-crossing in the loop gain? It is the highest frequency crossing which matters for loop stability. But generally it is a good idea to avoid double crossings entirely as they may be susceptible to conditional stability conditions.

    2- Yes, transient response = dynamic load response.

    3- Yes, the PWM jitter. For DCAP controllers it is normal to see ~200 ns of switching jitter. But if it's really excessive it might indicate a problem.