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UCC28070: how to measure the current loop (phase & gain margin)?

Howard Zou
Genius 12365 points
Part Number: UCC28070

Hi,

my customer would like to measure the bode plot of current loop of UCC28070 with loop analyzer.

But how could it be accomplished?

  • 0
    TI__Genius 13660 points
    Hi Howard,

    I have contacted one of my colleague to help here.

    Regards,
    Teng
  • 0 in reply to Teng Feng
    TI__Mastermind 34465 points

    PFC_LoopResponse.pdfHello Howard,

    The method for measuring loop response is detailed in the attached TI seminar document.

    Special conditions relating to the high output voltage are described in page 29

    Regards

    John

  • 0 in reply to Teng Feng
    TI__Genius 9140 points

    Hi Howard,

    Since UCC28070 do not sample PFC inductor current directly, and only sampling mos current to do the control. Can you advise customer to add a small resistor, for example, 10ohm between pin CSB and the negative pole of diode on the CT sampling circuit?

    I think it may be ok to do the current loop test at this point, and please make sure the GND should be connected to the same GND point of UCC28070.

    I attached the test point here.

  • 0 in reply to David Huang33
    TI__Intellectual 1960 points

    Hi David,

    Have you ever used this method to measure the current loop of UCC28070? The CSB test the MOSFET current, this current should be discrete. If add a disturbance here, can the circuit work well and show the correct Bode diagram?

    Regards,

    Lenna

  • 0 in reply to Lenna Yan
    TI__Genius 9140 points
    Hi Lenna:
    I do not test UCC28070 current loop before, I think UCC28070 should be working normally when you add the injection signal here. Please make sure that the amplitude of CSB is at around 3V, so the injection signal should be at around 1%-5% of the amplitude of CSB.I suggest start from 1% which means the injection signal amplitude is at 30mV, and then see the bode diagram, if you can not get clearly bode diagram, try to increase the amplitude of the injection signal.