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TPS92691: minimum soft start time

Ryuji
Guru 20090 points
Part Number: TPS92691

Hello,

Could you please let me know the minimum soft start time which we can set.

Cout=66uF, Vout=15V, ILED=2A , L=1.2uH or 1.8uH or 2.2uH

In the webench designer, the tss range is 1ms to 15ms.
Is the minimum soft start time is 1ms?

Best Regards,
Ryuji

  • 0
    TI__Mastermind 25500 points

    Hello Ryuji,

    Webench likely bases the minimum on the datasheet equation and would be the approximate time to fully charge the output capacitors and prevent any overshoot. You can go with less or even leave SS open if you really want to but depending on your circuit and all of your operating parameters you may have LED current overshoots at startup.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Guru 20090 points
    Hello Clint san,

    Thank you for the reply.

    If I calculate Css with the following conditions, the Css is negative value.
    What happens in this case?　Does overshoot occur?
    Should we use the device under conditions that the calculation of Css becomes positive?

    Best Regards,
    Ryuji
  • 0 in reply to Ryuji
    TI__Mastermind 25500 points

    Hello Ryuji-san,

    Css being calculated as negative just means that SS will charge and be out of the circuit before COMP even reaches the 0.7V SS clamp voltage so SS isn't really doing anything, it might as well be left open. Whether or not there is overshoot would depend on a lot of factors and would need to be tested on the bench. If there is overshoot and you want to get rid of it then yes, you would need to have a positive Css value to slow the turn-on.

    Regards,

    Clint