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TPS62861: what the difference between startup time in datasheet

Yuan Tan63
Expert 3280 points
Part Number: TPS62861

Hi,

customer want to find a part with small delay between Vin and Vout. Vin=5V, Vout=3.3V, Ioutmax=500mA. EN is connect with Vin through dividers. delay between Vin and Vout should be <500us.

I check TPS62861,

which one is the delay between Vin and Vout, 0.2ms or 1000us?

and when I want to find a buck or LDO with lower delay between Vin and Vout, which feature I should check? thanks.

Best regards,

Yuan

  • 0
    TI__Expert 3611 points

    Hi Yuan,

    If by time from Vin to Vout you mean the time between EN high and 95% of Vout, then you should sum the delay to start switching and the soft start time.

    Regards,

    Davor

  • 0 in reply to Davor Pavlovski
    TI__Expert 3280 points

    Hi Davor,

    so tstartup in Figure6 is equal to "internal fixed soft-start time" plus "EN high to start of switching delay" ? maximum 1.2us?

    omg, that's not OK for customers' requirement.

    when I want to find a buck or LDO with lower delay between EN and Vout, what feature it should have? soft start? thanks.

    Yuan

  • 0 in reply to Yuan Tan63
    TI__Expert 3611 points

    Hi Yuan,

    For your application of Vin = 5V; Vout = 3.3V; Ioutmax = 0.5 A; start-up time <= 500us. I can recommend the TPS62063 with fixed Vout at 3.3V. It has a start up time of 500 us.

    A converter with a faster start-up time would be the TPS62237 at 100us, however the peak output current is 0.5A which does not give much margin given your design specs.

    Also regarding the soft-start feature, the reason why the converters are soft-started is so the inrush current at start-up is lower and this actually increases the start-up time.

    When looking for something with a specific start-up time, always check the start-up time which is the "Time from active EN to reach 95% of VOUT" in some datasheets this is given as a sum of the start-up delay (EN HIGH to start of switching delay) and the soft-start time.

    Regards,

    Davor

  • 0 in reply to Davor Pavlovski
    TI__Expert 3611 points

    Hi Yuan,

    Did I manage to answer your question or do you still have some uncertainty about the topic?

    Regards,

    Davor