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TPS7A80: Confusion on start-up time

MINKYUNG KIM
Expert 1250 points
Part Number: TPS7A80

Hi team,

I'm confusing startup time in TPS7A80 device.

From the description and internal block diagram below, t_STR would be 760us with 1 nF of C_NR (t_STR = 76,000*1n), which has no issue because the quick-start switch will be closed during 2 ms.

But I don't have any idea on how the t_STR would be 1.5 ms as noted below. Is there any other internal block or other factors that is not described in the DS but may have effect on start up operation?

Please help my understanding. Thank you. 

  • 0
    TI__Mastermind 44770 points

    Hi Minkyung,

    The clarification on equation 1 is 'whichever is smaller':

    With CNR at 10nF the datasheet shows a typical of 1.6ms. If you put a CNR of 47nF, equation 1 is no longer valid. What this means is that for ~2ms the quick-start circuit will have VOUT while the switch is closed and once it opens, the slope will be a function of the RC time constant formed by the internal 225k resistor and CNR.

    I hope this answers your question.