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TPS23751: About softstart function

Satoshi
Guru 19495 points
Part Number: TPS23751

TPS23751 datasheet P34 is described softstart function, please let me know about two points below;

①I think that Css, Rss, and Dss are mean soft start setting.

　Is there equation for soft start time by Css, Rss, and Dss? 

②If not careful softstart, are Css, Rss,Dss left open no problem?

Best regards,

Satoshi

  • 0
    TI__Mastermind 40110 points

    Hi Satoshi-san,

    1. At startup, Css will charge up through Rss. So the secondary side softstart will be related to time constant Rss x Css. Dss is used such that the RC does not effect the loop.

    Note that typically there should be a diode across Rss (cathode at the output) to discharge Css during shutdown. This is used on all our PoE EVMs and TI Designs.

    2. If Css, Rss, and Dss are not populated, then you may see output voltage overshoot during startup.

    Regards,

    Darwin

  • 0 in reply to Darwin Fernandez
    TI__Expert 5615 points
    Satoshi-San,

    I wanted to check in with this thread as we have heard back from you in some time. Please let us know if there is anything else we can do to assist...otherwise, we are going to assume this thread is resolved.

    Thank you for your interest in PoE products from TI,