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TUSB8041: Power sequence requirement (datasheet conflicts)

Dave Selig
Prodigy 40 points
Part Number: TUSB8041

Section 7.6 of the datasheet states that Td1 requires VDD33 stable before VDD is stable.  However, footnote 2 states that VDD must be stable >= 10us before VDD3 if using the 1 uF GRSTn capacitor.  These two requirements appear to be in conflict.

Also, 9.2.1.2.7 states "The 1 uF capacitor on the GRSTN pin can only be used if the VDD11 supply is stable before the VDD33 supply."  This again appears to be in conflict with the first statement in 7.6.

Finally, the reference platform schematic (http://www.ti.com/lit/pdf/sllu198

  • 0
    Prodigy 40 points
    My message appears to have been truncated...

    Finally, the reference platform schematic (www.ti.com/.../sllu198.pdf) shows 1.1V being generated from 3.3V (see U6). This agrees with the first part of 7.6 but is in conflict with the other two statements.

    Please confirm which implementation is correct when using the 1 uF capacitor on GRSTn:

    1) 3.3V -> 1.1V
    or
    2) 1.1V -> 3.3V
  • 0 in reply to Dave Selig
    TI__Expert 7395 points
    Hello Dave,

    If using a passive reset (just a cap on GRSTz) the recommendation is to supply VDD (at least 10uS) before VDD33.

    If you have an active reset, then there is no power-on relationship between VDD and VDD33; however your active reset would need to ensure that the GRSTz terminal is asserted (low) for at least 3 mS after both power supplies are stable.

    On the datasheet Td1 makes reference to both footnotes 1 and 2; footnote 1 is intended to clarify that the 3mS power on delay would be needed when having a configuration where VDD33 is enabled before VDD. Sorry if that wasn't clear enough.

    Finally I would like to recommend to use TUSB8041A as a replacement for TUSB8041. Both devices are pin to pin compatible, however TUSB8041A is compliant with a newer version of the USB spec (3.0 vs 3.1) and provides support for additional battery charging modes (ACP1, ACP2)

    Regards,
    Jorge
  • 0 in reply to Jorge Llamas (SWAT)
    Prodigy 40 points
    Hello Jorge,

    Thanks for the reply. I will look at the TUSB8041A.

    Based on your response, it sounds like the Evaluation Module design would violate the requirement. It has a 1uF cap on GRSTn, and generates +1.1V (VDD) from the +3.3V (VDD33) power rail. See C3 on pg 9 and U6 on pg 11 of www.ti.com/.../sllu198.pdf

    Can you confirm?

    Dave
  • 0 in reply to Dave Selig
    TI__Expert 7395 points
    Dave,

    That is correct. The evaluation module isn't following this guideline.
    This is something we may need to change on future revisions of the board.

    Regards,
    Jorge
  • 0 in reply to Jorge Llamas (SWAT)
    Prodigy 40 points

    Thanks for confirming!