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LMR16030: Question of Soft start spec

Lee, Sam
Expert 6045 points
Part Number: LMR16030

Hi team,

Can you answer the follwoings questions for LMR16030?

1. For LMR16030SDDAR, what is the max and min. spec of tss(ms)= (Css x Vref) / Iss? Or is there any guideline?

2. For LMR16030PDDAR,

      -. is it okay if PGGOD pin is connected with MLCC Cap - GND like the version of soft start?

      -. is it okay to leave PGOOD pin floating?

Thanks,

Sam Lee

  • 0
    TI__Mastermind 25590 points

    Sam Lee,

    1. The guideline is mostly just "pick a time that works for your system." The PGOOD version has internal SS at 4ms so I'd start there.  Things to consider:

    • SS Cap too small may give too much inrush current at startup
    • SS Cap too large will slow down startup. This applies to power-on, thermal reset, and other device disable/enable. There is no theoretical limit to how big this cap can be.

    2. PGOOD is just a signal out to tell other circuitry that P is GOOD. Typical operation has a pull-up resistor on this pin. Adding a cap will just slow down and smooth out this signal.  You can leave it floating if you do not need to use the PGOOD signal for anything else.

    -Sam J