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LM76005-Q1: Question about switching waveforms.

David Kim2
Expert 2945 points
Part Number: LM76005-Q1

Hi

If you look at the switching waveform, there is a duty change in the middle.
So I tried both pfm/pwm modes and they were the same.
Normal waveform?

And in PWM mode, inductor heat was generated, but when I changed to PFM mode, the heat decreased. Can you explain why?

Thanks

  • 0
    TI__Mastermind 35750 points

    Hello David,

    No, not normal, can you please share schematic and specification you design to.  Thanks.

    David.

  • 0 in reply to David Baba
    Expert 2945 points

    Hi David

    Please refer to below.

    -spec-

    Input: DC12V~36V

    Output: 8.37V 2A

    Thanks

  • 0 in reply to David Kim2
    TI__Mastermind 35750 points

    Hello David,

    The waveform's provided suggest your loop is unstable.  Looking at your frequency selection, you have 440kHz, calculating the ripple current in the inductor, you have a peak to peak current of 0.5A.  For a 5A output current device employing peak current mode control, this appears to be too low.  Suggest changing the inductor to 4.7uH and see if that helps. 

    Another thing to look at is your input filter.  You will need a 47uF cap at the input with and ESR of 0.3ohm to dampen, please try each of these things to stabilize the loop. 

    Hope this helps.

    David.