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LM5026 Sync pin noise solution

Huai Wei
Prodigy 20 points

We use TI PWM controller LM5026MTX in a 1/16 brick DC-DC converter module with 36-75V input, 12V/8A output. We noticed that the sync pin is noise sensitive and the noise at the sync pin could cause power MOSFET failure. The sync pin is currently NC. We can reduce the noise sensitivity by connecting a 33pF cap or a 47k resistor. Since the data sheet doesn't refer to do so, we would like to confirm whether the solution is safe. Could you please give answers to the following questions?

1.Could the sync PIN of LM5026MTX be floated?

2.Can we connect a 33pF cap or 47K resistor between sync PIN and Ground？

3.Do you have any comment on the sensitivity of the sync pin that affect the stability of the DC-DC converter?

  • 0
    TI__Mastermind 31580 points
    Hi Huai,

    I have asked one of our applications engineers to review your post, you should see a response soon.

    Regards

    Peter
  • 0 in reply to Colin Gillmor
    Prodigy 20 points
    Hi Colin,
    Could you please answer my questions?
    .Could the sync PIN of LM5026MTX be floated?

    2.Can we connect a 33pF cap or 47K resistor between sync PIN and Ground？

    3.Do you have any comment on the sensitivity of the sync pin that affect the stability of the DC-DC converter?

    Thanks,

    Huai Wei
  • 0 in reply to Huai Wei
    TI__Mastermind 25570 points
    Hello Huai

    My apologies. In my earlier attempt at a response I pressed the 'Reply' button too soon and posted the greeting only. I went back and posted a full reply but that seems to have become lost somewhere.

    Anyhow. To answer your questions

    1/ Yes, you can leave the SYNC pin floating. Do minimise the size of any copper PCB traces at this pin so that it does not pick up unwanted electrical noise.

    2/ I would suggest the 33pF capacitor to reduce the noise sensitivity of this pin. A resistor may work as well but it will draw a small current from the pin. The pin can source only 200uA.

    3/ I can't really give you any comment on the pin sensitivity. It is a synchronisation input / output pin and in order to function it must have a wide bandwidth.


    Regards
    Colin