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TPS40200 Soft-Start Time Calculation

takishin
Expert 2360 points
Other Parts Discussed in Thread: TPS40200

TPS40200 Soft-Start Time Calculation

The data sheet mentions the slow-start time should be longer (slower) than the time constant of the output L-C filter.

My questions are;

(1)Does the time have a maximum value?

(2)Are there any conditions in order to decide on the time? (load etc.)
(If it is large enough, is it satisfactory? )


Thanks in advance.

takishin

  • 0
    TI__Prodigy 310 points

    Team,

    Will you please give your response to this inquiry ?

    Regards,

    Masamichi Ikeda

  • 0
    TI__Mastermind 35115 points

    Hi Takishin,

    Please see below.

    1. There is no maximum value. The tradeoff to consider is a longer soft-start time will cause a

    2. In addition to the output L-C filter time constant, another important factor to consider is to make sure the startup time is long enough to avoid tripping hiccup current limit during startup. During startup there is effectively an additional load on the output from charging up the output capacitors. The startup time should be long enough to keep the effective load current below the current limit. The effective load current is the load current plus the current charging the output capacitance. The current charging the output capacitance is equal to I = C * dV/dt. C is the output capacitance, dV is the output voltage and dt is the soft-start time.

    Best Regards,
    Anthony

  • 0 in reply to Anthony F
    Expert 2360 points

    Hi Anthony,

    Thank you for your answer.

    About your answer #1;

    What will  a longer soft-start time cause ?

     

    Best Regards,

    Takishin

  • 0 in reply to takishin
    TI__Mastermind 35115 points

    A longer soft start time causes a longer hiccup time period. This means it will wait a longer period to try again after current limit is hit. This usually isn't an issue but is something to be aware of.

  • 0 in reply to Anthony F
    Expert 2360 points

    Thanks for the response. 

    takishin