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TPS6521855: WAIT_PWR_EN/termination of unused pins

Shota Mago
Expert 6580 points
Part Number: TPS6521855

Hi team,

My customer will use TPS6521855 and he is asking some questions.

  1. Datasheet 42 page shows when PGOOD becomes Low due to output fault, the device enters WAIT_PWR_EN state after RECOVERY state.
    If PWR_EN remains high all the time, the device will go into ACTIVE state and each power supply will start up again. Is this understanding correct?
    Or does it stay in the WAIT_PWR_EN state because it is monitored at the rising edge of PWR_EN?
  2. How should they terminate following unused pins?
    PB, nWAKEUP, nINT, GPO2, GPIO3, IN_LSx, LSx, PFI, nPFO

Best regards,

Shota Mago

  • +1
    TI__Genius 15050 points

    Hi Shota,

    1) Your understanding is correct. When the device reaches WAIT_PWR_EN the rails should activate again, assuming the fault has been fixed. As long as you have PGOOD asserted high at this point, a high PWR_EN will allow you to move back to ACTIVE state.

    2) For pin terminations:

    • PB should still be tied to IN_BIAS through 100k pull-up resistor so that no reset signal is seen from this pin during operation
    • nWAKEUP is not involved in any state transitions so I believe it can be left floating if not connected to SoC
    • nINT is also not involved in any state transitions. I think you can leave this pin floating. Interrupts can be masked for extra security.
    • GPIO2 and GPIO3 can be left floating
    • IN_LSx and LSx pins can be left floating since they are not included in the voltage monitoring
    • PFI and nPFO pins can be left floating. Make sure that the OFFnPFO bit in the CONTROL register is set to "0" so that the power fail comparator doesn't control the power down sequence (see Section 7.3.1.9 of the datasheet for more information).

    If you have any issues with these pins or the power sequence let us know here on E2E.

    Regards,

    James

  • 0 in reply to James Steenbock
    TI__Expert 6580 points

    Hi James,

    Thanks for your answer.

    Just for double check, as for question #1, if PWR_EN and PGOOD are high(fault has been fixed), the device automatically exit WAIT_PWR_EN and becomes ACTIVE(toggling PWR_EN is NOT needed to exit WAIT_PWR_EN). Is this correct?

    Best regards,

    Shota Mago

  • 0 in reply to Shota Mago
    TI__Genius 11020 points

    Hi Shota,

    The product expert will get back to you tomorrow, today is Memorial day in US. 

    Thanks.

    Regards,

    Tomi Koskela

  • +1 in reply to Shota Mago
    TI__Genius 15050 points

    Hi Shota,

    That is correct. If PWR_EN is high the device will automatically move from WAIT_PWR_EN to ACTIVE state.

    Regards,

    James

  • 0 in reply to James Steenbock
    TI__Expert 6580 points

    Hi James, 

    Thanks for clarification!

    Regards,

    Shota Mago