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Hi, I have a question about cutoff frequency and cross-over frequency in bode plot of buck converter.

Yunsik Chung
Intellectual 1150 points

Hi,

I was studying buck converter's stability and wonder if cutoff freq and cross-over freq are same frequency.

In addition, 

In the lecture, he said switching frequency should be 10 times of cutoff frequency.

Can i use the term cross over frequency instead of cutoff frequency?

Also, i wonder why switching frequency should be way bigger than cut off frequency in a mathematical way.

Thanks,

  • 0
    TI__Expert 3135 points

    Hi Yunsik,

    1.cut-off frequency is same as cross-over frequency

    2. The cut-off frequency corresponds to a point where the gain is 0dB, we want a stable and DC output voltage. Therefore, our system needs to amplify the low-frequency signal and suppress the high-frequency noise, the biggest high frequency noise is the switching frequency, so switching frequency should be bigger than cut off frequency.

    Best regards,

    Kevin

  • 0 in reply to Kevin-Cheng
    TI__Expert 3135 points

    Hi Yunsik,

    Since I have not received your reply for several days, I will turn off this item. If you have further question, you can reply it again.

    Best Regards,

    Kevin

    If this answers your question, Please click "This resolved my issue" button.
    ____________________________________________
    TPS62810-Q1 – New Automotive 6Vin, 2.25MHz buck family with 1% accuracy and SYNC-pin. 1-2-3-4A options.
    Smallest 2x3QFN package with wettable-flanks for optical PCB inspection.

  • 0 in reply to Kevin-Cheng
    TI__Intellectual 1150 points

    Hi Kevin,

    Sorry for the late reply.

    Your answer was really helpful and i could understand it fully.

    Thank you for your kind reply again.

    Thanks,

    Yun