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TUSB8020B: interface power-up issue

James Guyton
Prodigy 110 points
Part Number: TUSB8020B
Other Parts Discussed in Thread: TPS65220

Tool/software:

Hi all, I'm trying to chase down why we are observing an issue where if a TUSB8020B is being supplied from a TPS6522053, we are having some issues with the power on sequence. Removing FB41 allows the TPS6522053 to complete the power up sequence, and bring up the processor.

Prior to removing FB41 (2nd shot, CH4 is 0V85, possible reverse voltage): 

After removing FB41 (CH4 is 0V85): 

Is there an idea of what is possibly happening here?

Thanks,

James


Links for earlier associated/related questions/issue resolutions in the design:
TPS65220: TPS6522053RHBR - no power from supply rails (AM64X)

 AM6442: Schematic review request - TPS6522053 unable to fully ramp up BUCK2/BUCK3 outputs (1V8, 1V1) 

  • 0
    TI__Guru*** 149200 points

    Hi James:

        When 3.3v is on first, there is leakage  on 1.1v supply , which could cause PMIC part TPS65220 turn off. You may need to use LDO to avoid such issue.

    Best

    Brian

       

  • 0 in reply to Brian Zhou
    Prodigy 110 points

    Hi Brian,

    Would you expect any particular problems if I fed 1V1 in from a bench supply on the U34 side of FB41, after the 3V3 comes up (or for that matter, feeding it 1V1 before the 3V3 comes up)?

    And would you expect that a TLV75511 would be sufficient as an LDO for supplying it 1V1? 
    Thanks,

    James

  • 0 in reply to James Guyton
    TI__Guru*** 149200 points

    Hi James:

       if TLV75511  can meet dropout voltage of 1.1v output, it should work.

    James Guyton said:
    Would you expect any particular problems if I fed 1V1 in from a bench supply on the U34 side of FB41, after the 3V3 comes up (or for that matter, feeding it 1V1 before the 3V3 comes up)?

    I don't' see any issue.

    Best

    Brian