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LM5155: Maximum Softstart time

Yusuke Mukuno
Expert 7395 points
Part Number: LM5155
Other Parts Discussed in Thread: LMP8646

Hi expert,

Do you have maximum requirement for Softstart?

My customer want to set several sec for softstart time.

 From datasheet Equation 3

Can they select over 10uF capacitor for SS pin?

Thanks

Muk

  • 0
    TI__Genius 11215 points

    Hello Muk,

    Thank you for your message. The responsible person is not in the office today but she will answer to your question tomorrow. 

    Sorry for the inconvenience, 

    Elisabetta

  • 0
    TI__Guru 61215 points

    Hello Yusuke,

    I am not aware of a limit for the SS capacitor, but I need to check this more in detail. Would you please explain why the customer wants to have such a long softstart time?

  • 0 in reply to Brigitte
    TI__Expert 7395 points

    Hi Brigitte-san,

    Thank you for your supporting.

    The load is large Fan. Customer have to care about startup current of Fan. 

    LM5155 have current limit. The startup current might be limited by current limit, because current limit should work during startup, 

    Is it correct? 

    If they have consider about the current limit accuracy, we may be able to propose LMP8646 (current limiter).

    Also, Could you please confirm about maximum SS capacitor?

    Thanks

    Muk

  • 0 in reply to Yusuke Mukuno
    TI__Guru 61215 points

    Hello Yusuke,

    Please excuse the very slow response time. This thread somehow got overlooked.

    For this application, I think the LMP8646 would be the better choice instead of using the SS capacitor to limit the current.

    Please give me some further days to get back to you according the SS capacitor.