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LM5150-Q1: Duty cycle limit at cycle-by-cycle current limit in start-stop mode

DY Ko
Expert 4160 points
Part Number: LM5150-Q1

Hello team,

My customer want to know how much the duty cycle was limitted or decreased when entering the cycle-by-cycle current limit in the start-stop configuration.
Please expalin how to operate the the cycle-by-cycle current limit of LM5150-Q1including calculation.

Best regards,
DY

  • 0
    TI__Guru 68495 points

    Hi DY,

    Thank you for posting.  The cycle-by-cycle current limit is implemented with a comparator, which compares the sensed current with a fixed threshold.  It is equivalent to clamping the COMP voltage on the PWM comparator by the same threshold, then you can use the same comparator to achieve both PWM and cycle-by-cycle limit.  

    In most ICs, a separate comparator is used for peak current limit. When the sensed signal hits the threshold, it truncated the duty cycle right away, earlier that the regular PWM comparator.  Note that the current waveform has a ramp on top, and the higher the current the earlier the ramp can hit threshold, and the earlier to cut the duty cycle short.  

    Hope this clarifies.

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    TI__Expert 4160 points

    Hello Youhao,

    Thanks for your quick response.
    Would you please send me the relevant apps note or technical document including more detailed explanation?

    Best regards,
    DY

  • 0 in reply to DY Ko
    TI__Guru 68495 points

    Hi DY,

    This is a fundamental function like the PWM comparator, and similar to PWM comparator, so well known that I don't think anybody in our group has the materials just discussing it. I just searched by Google and a few articles show up but I cannot mention those here owing to copyright.  You can read online, I believe.  You may also ask your customer to find a power electronics text book which may discuss about this.

    Thanks,

    Youhao