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TPS659037: Discrepancy in measured behavior of LDO1 and LDOUSB

Michael Shklyarman
Genius 12740 points
Part Number: TPS659037
Other Parts Discussed in Thread: AM5728

Champs,

On an AM5728 customer-designed board utilizing the above PMIC (P/N TPS6590377ZWS) the power up sequence has been measured and compared to the one documented in the user guide: http://www.ti.com/lit/ug/sliu011e/sliu011e.pdf 

  • 0
    TI__Genius 12740 points
    Looks like the second half of the question has been cut off upon posting. here it goes:

    The "Figure 7. OFF2ACT Sequence of TPS6590379ZWSR" in the user guide shows LDO1 and LDOUSB ramping up simultaneously. In the measurement we observe ~ 200 us delay between the two: LDO1 comes up first followed by LDOUSB.

    Questions:
    1. Is this expected?
    2. Can this cause any issues in processor's operation? (none have been observed so far but the product is in prototype stage)

    thank you
    Michael
  • 0 in reply to Michael Shklyarman
    TI__Genius 16410 points
    Hi Michael,

    Yes, this is expected. LDOUSB has a fixed 215us internal start-up delay. So while they are enabled at the same time by the digital controller, you will see LDOUSB ramp up later. This doesn't have any issues to the processor, since these rails are in the same time slot, meaning they can ramp up in either order as long as they complete before the next time slot.

    Regards,
    Karl