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TPS92513: about start up rise time

ACGUY
Guru 11170 points
Part Number: TPS92513
Other Parts Discussed in Thread: TPS92515

Hello E2E,

I evaluating the this device on EVM.
It seems like, this device has unevenness for start up rise time.
I think that this cause is tolerance of gM.

  -  gM is typically or higher -> Response speed is High -> rise up time is short
  -  gM is less than typically -> Response speed is Low -> rise up time is long

Is this correct?

Regards,
ACGUY

  • 0
    TI__Mastermind 25500 points

    Hello ACGUY,

    This device starts up open loop using just narrow switching pulses until COMP is charged to 0.7V (see the Start-Up section in the datasheet). Since it is open loop the startup time can be unpredictable at times. For example, COMP can hold charge for some time. So if you turn it on for the first time in a while it will have one startup time, then if you turn it off and on again really quickly COMP can start at a higher voltage and shorten the time. gM has something to do with it, but only after COMP reaches 0.7V and it enters regulation mode.

    The way it starts is good for reducing inrush current and ensuring it always starts properly, but as I mentioned the time can be unpredictable and depends on many factors. If you need a very predictable startup time and profile you may want to check out the TPS92515.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Guru 11170 points

    Hi Clint,

    Thank you for response.
    I was measured two devices at same board. I found the difference ILED.
    Device-B is slow response, A is typically speed.

    What do you think cause?

    Regards,
    ACGUY

    TPS92513.pdf

  • 0 in reply to ACGUY
    TI__Mastermind 25500 points

    I see. In that case it will vary with the difference in gM but also other factors. The tolerances of the COMP cap, input cap, output cap, Rds(on), L, minimum ON time, etc... will all come into play as well since the startup is open loop. It is a very reliable startup method but not very consistent.

    Regards,

    Clint