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LM3478 SOFT START

Jorge Tornero
Prodigy 90 points
Other Parts Discussed in Thread: LM3478, TPS40210, LM5121, LM5022

Hello,

I have to use LM3478 but I need a much more soft start time (100ms.....500ms) , Is there any way to get it?

thank you

  • 0
    TI__Intellectual 1775 points

    Hi Jorge,

    Not really, at least not easily. There are ways to artificially slows the start-up by using a large feedforward capacitor on the feedback network but I doubt it would work for the range you are looking for.

    You could force a small source current ramp on the FB pin (from high to low) in order to pull FB artificially high. As the source current decreases, the controller will compensate by forcing the output voltage higher until the source current is null and the output will then be the full programmed output voltage.

    You could also try forcing COMP low and very slowly releasing it which would starve the output from current to recharge the output capacitor but that will not really work unless there is load on the output.

    These are just ideas you can try but they will likely need additional logic and circuitry and proper considerations for the specific system to get right.

    Have you considered using another device that might be more suitable for your needs such as LM5022, LM5121 or TPS40210?

    Best Regards

  • 0 in reply to Florent Boico
    Prodigy 90 points

    hello Florent,

    thank you for your answer. You are absolutely right

    I was obsessed with that integrated because I already have it.

    I'll use your first recommendation LM5022.

    Thank you very much again and regards