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TPS61085: Crossover frequency

Pjs
Intellectual 870 points
Part Number: TPS61085

Hi, 

Can you advise how best to select the crossover frequency for the compensation on the TPS61085. It's been suggested in the past that a good rule of thumb is to aim for 1/10th of the switching frequency but I'm struggling to get anywhere near this in Webench. 

Entering the example compensation components in the datasheet also results in very low crossover frequencies. 

Thanks

 

  • 0
    TI__Intellectual 2645 points
    Hi Pjs,
    Crossover frequency influences dynamic behavior, like load transient. Higher Crossover frequency, better dynamic behavior.
    For the stability, you need to guarantee phase margin>45deg and gain margin>10dB.
    First, we need to guarantee stability and then make crossover frequency higher. Normally crossover frequency could up to 1/10.
    You could design compensation by Webench.
  • 0 in reply to Jing Ji
    Intellectual 870 points
    Hi Jing Ji,

    Thanks for the reply.

    Does this mean that as long as you have decent phase & gain margin, then whatever the cross over frequency the system will be stable?

    Using the datasheet compensation suggestions in Webench, I end up with a cross over freq. of around 5kHz for a 1.2MHz switcher and as a result the transient response is quite poor. Could someone take a look at my Webench simulation and see if I'm doing something wrong?

    Thanks
  • 0 in reply to Pjs
    TI__Intellectual 2645 points
    Hi Pjs,
    You could share Webench files with me. I could check it for you.
  • 0 in reply to Jing Ji
    Intellectual 870 points

    Thanks - can you provide and email address so I can share these offline?