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TPS7A33: Figure 29 startup time plot shows 20 ms for CNR/SS = 0 nF

John Haraguchi
Prodigy 250 points
Part Number: TPS7A33

Figure 29 shows a 20 ms startup time with no capacitance on CNR/SS. Is this correct or should the plot include an event trigger at t = 20 ms (i.e. enable asserted, input voltage applied)?

Based on information in other parts of the datasheet, I’m don’t think the startup time is really 20 ms for this condition but if I only looked at Figure 29 I would think it was.

Thanks,

John

  • 0
    TI__Mastermind 23361 points

    Hi John,

    Figure 29 should have shown the Vin change on the same plot as Figure 27. Based on the soft-start calculation, I would say that in Figure 29, Vin is up at around 20ms, then the startup time calculation should actually be from 20ms. For the Css=0, the startup time should be within a few mili-seconds; it's difficult to see in the plots due to the large time scale.

    I agree, Figure 29 is confusing and hope my explnations help. 

    Regards,
    Jason Song

  • 0 in reply to Jason Song
    Prodigy 250 points

    Hi Jason,

    Thanks for the reply on this one.

    I will make a note in my datasheet that Vin is being applied at t = 20 ms.

    Thanks,

    John