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LM5122: LM5122 and power triggering during start up

Babak Manou
Intellectual 420 points
Part Number: LM5122
Other Parts Discussed in Thread: LM5121

Hello 

I have designed a 24V boost converter using LM5122 and following the schematic and values given in the datasheet. I have a strange problem with my circuit. When I turn my power supply on, the power supply starts to trips for about 15 seconds (current limiter doesn't let to much current pass and I think that is why it triggers! it's limit is on 2A). After that circuit is stable and I have 24V output.
My initial guess is an inrush current required to charge up all 4 capacitors (330 uF each) and energize the circuit. Is there any way we can avoid it? On a different test, I connected the battery as a power supply but it blew out my Mosfets and a couple of traces in my board. I am in a process of redesigning the converter with a more efficient layout following the recommended layout given in the datasheet. A picture of the old layout and a MOVIE from error is attached.
Cheers,
Babak
  • 0
    TI__Guru 68335 points

    Hi Babak,

    The boost converter does not have inrush limit mechanism during initial output capacitor charging. To prevent your problem, you should choose the LM5121, which has the inrush limit function. 

    Thanks,

    Youhao Xi,  Applications Engineering

  • 0 in reply to Youhao Xi
    Intellectual 420 points

    Hi Youhao,

    At this point in the design, it is difficult to change the IC and change the layout. I went through the datasheet of the new IC and noticed that two pins are different in this IC. PIN1 is DS and PIN 2 is DG while in LM5122MH there are SYNCOUT and OPT accordingly.

    This Ic is selected based on the recommendation of TI engineers. We need 7A at 24V, that is why we are using this IC.

    I am not sure if it is caused by inrush current! that was just a thought! It may be caused by other reasons that I am not aware of!

    Thanks,

    Babak

  • 0 in reply to Babak Manou
    TI__Guru 68335 points

    Hi Babak,

    Understood about the difficulty to change IC.  I noticed from your previous post that your power supply has a current limit of 2A.  It cannot support your targeted power level. Please measure the input current. You need to try on a larger power supply.

    Thanks,

    Youhao

  • 0 in reply to Youhao Xi
    TI__Guru 68335 points

    May I assume this issue has been resolved so I can close this thread here?  You can always re-open it by adding a new post.


    Thanks,

    Youhao