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Original question:

TPS549A20: Soft Start and PGood timing

TPS549A20: Disable Soft Start

Russell Wetherley1
Expert 4255 points
Part Number: TPS549A20
Other Parts Discussed in Thread: TPS549B22, TPS54672

Hello E2E,

Is it possible to disable the soft start on the TPS549A20?  What's the fastest way we can boot up to regulator?

My customer is looking for something that can rise at ~75mV/us (33us for 2.5V; 16us for 1.2V).  This is INCREDIBLY FAST!!!!!  I don't think we can do it but let me know if I'm wrong. :)  Any other regulators that could work? 12Vin, ~6A out.  TBD on Cout.


Russell

  • 0
    TI__Mastermind 48200 points

     

    No, we can not disable the soft-start of the TPS549A20.

    I can't think of any regulator whose soft-start is designed to start-up that fast, and I am not sure that many regulators would track the reference voltage rising that fast.  You could likely use a converter that allows an external reference voltage, then hold the reference voltage at zero while the soft-start completes, then raise the external reference voltage at the desired ramp-rate.

    Yes, this is extremely fast.  75mV/us requires 1A of charging current for every 13.3uF of output capacitance, so depending on how much output capacitance is used, it might require a lot more than 6A of output current capability just to bring up the output voltage.

    It's overpowered for a 6A load, but the TPS549B22 is a 25A converter that offers an external reference voltage option by selecting the external reference via PMBus and inputting the external reference voltage to the TRK pin.

    The TPS54672 is a 6-A synchronous BUCK with an external reference voltage, but it's only rated for 6V inputs.