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LP8733: What happens if the power-up sequence is interrupted?

adevries
Intellectual 945 points
Part Number: LP8733
Other Parts Discussed in Thread: TPS6521825

Hello,

I'm interested in using the LP873347 in a circuit I am making, and I have a question about the power-up and power-down sequence this chip goes through. I understand that if EN goes high, the chip will start the power-up sequence. However, what if EN goes low in the middle of the power-up sequence? Will the IC interrupt the power-on sequence and immediately begin the power-down sequence? Or will it finish the power-up sequence before starting the power-down sequence? 

What about the opposite situation? If EN goes low, the IC will start the power-down sequence. But what if EN goes high in the middle of the power-down sequence? Will it immediately start the power-up sequence? Or is the state of EN masked for a certain period of time after the power-down sequence has started?

Thanks

  • +1
    TI__Genius 11020 points

    Hello Adevries,

    LP8732 will interrupt the startup sequence and begin the shutdown sequence once the EN goes low. Same thing for the opposite situation. EN pin digital filter is set at 3us, so it filters shorter pulses away. 

    Thanks.

    Regards,

    Tomi Koskela

  • 0 in reply to Tomi Koskela
    Intellectual 945 points

    Hi Tomi,

    Thanks for the reply. So, if there is noise on the EN pin, it's possible the device will interrupt the shutdown sequence to start up, then interrupt the startup sequence to shutdown, then interrupt the shutdown sequence to startup, etc... until the voltage on the EN pin stabilizes, right? Do you know if the TPS6521825 exhibits the same behavior with its PWR_EN pin?

  • 0 in reply to adevries
    TI__Genius 11020 points

    Hello Adevries,

    Basically yes, but the 3us filter time is set to avoid noise causing continuous triggering of EN. Additional Schmitt trigger can be also used to avoid this situation. There is also diagram in the datasheet that depicts the short EN pulse case, diagram 16. 

    I'm looping in our expert on TPS6521825 to help with that. 

    Thanks.

    Regards,

    Tomi Koskela