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TUSB4041I: 3.3V is back feeding onto 1.1V rails

Benjamin Blanton
Prodigy 50 points
Part Number: TUSB4041I
Other Parts Discussed in Thread: TPS65220,

Tool/software:

Hi, we're using the TUSB4041IPAPR and TPS65220 is the PMIC for our processor.  This PMIC design has 3.3V rail coming up before the 1.1V rail, which looks fine from the datasheet as long we come out of reset after the rails have settle.  The hub works as designed.  The issue we're having is that the 3.3V on the Hub is back feeding onto the 1.1V before the 1.1V rail has been turned on by the PMIC.  We're seeing around 0.25V on this rail and in some edge cases this voltage is high enough that the PMIC will not turn on.  

  • 0
    TI__Guru*** 145435 points

    Hi Benjamin:

      first not recommend switching DC-DC converter which adding low frequency jitter  to the hub.

        Is  this PMIC  turned on by EN pin ? how the output affect PMIC  enable or disable?

    Best

    brian

  • 0 in reply to Brian Zhou
    Prodigy 50 points

    I'm not sure the relevance of this question.  The PMIC turns on when the board is initially powered.  3.3V comes from an independent supply, while 1.1V is created by the PMIC.  The PMIC will not start if there is a residual voltage any rail and TUSB4041I is creating a 0.25V voltage through the hub.  We confirmed this.  This seems like a design defect.  Please advise on how to proceed.

  • 0 in reply to Benjamin Blanton
    TI__Guru*** 145435 points

    Are there any other loading on 1.1v supply?

    i'm not PMIC  expert, let me check with TI PMIC group if it's normal  behavior with 0.25v residual voltage

    with 0.25V leakage on 1.1v of TUSB4041, you may need to use normal LDO device to get 1.1v.

    Best

    brian

  • 0 in reply to Brian Zhou
    TI__Guru*** 145435 points

    Hi Benjamin:

        I saw you post on E2E about  TPS65220. 

        Can you add a delay  for 3.3v  between TPS65220 and  TUSb4041 to make sure TPS65220  turned on first before 0.25V on 1.1v?

        If can't ,  may need to use other Vbus switch with EN pin.

    Best

    Brian