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TUSB4041I: VDD SUPPLY RAMP REQUIREMENTS (1.1V)

f bentley
Prodigy 20 points

Part Number: TUSB4041I

We currently use TI’s TUSB4041I USB hub in one of our designs. We use a fast transient response DC- DC reg to provide the 1V1 (VDD) required by the  TUSB4041I. However the ramp up time for this rail is too fast for the requirements stated on the TUSB4041I datasheet. We’ve tried adding caps to the 1V1 rail to slow it down but just cannot get it slow enough for the values on the TUSB4041I datasheet, 0.2 to 100ms. We are getting about 70uS to 80uS VDD ramp up time.

I wanted to know if this ramp up time is actually an issue for the UDB hub or not. If so, what are the implications?

 

Thanks

  • 0
    TI__Guru**** 155010 points
    how about 3.3v ramp? any delay between 1.1v and 3.3v?
  • 0 in reply to Brian Zhou
    TI__Guru 64326 points
    Hi,

    Generally we have only seen issues with slow ramp time and not fast rise times on TUSB4041I. I would ensure you are still observing the the delay between 1.1V and 3.3V rials with respect to each other (td1) and GRST reset (td2).
  • 0 in reply to Malik Barton57
    Prodigy 20 points

    Thanks guys,

    We have observed the 1V1 and 3V3 rail requirements. according to the datasheet, the 3V3 rail should be stable before the 1V1 rail is stable. In our design, the 1V1 is generated by the 3V3, so we have no issues here. 3V3 will always be up first. The datasheet also states that The VDD33 (3.3V) and VDD (1.1V) have no power-on relationship unless GRSTz is only connected to a capacitor to GND. In our design, GRSTz is controlled by a GPIO. Therefore, I believe no issues here as well.

    Thanks again