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USB OTG power rail schematic

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  • USB OTG power rail schematic

    Hi all! Hope you are feel good.

    Many examples connect net "+5V" from micro USB conector directly to +5V power net, or through the power switch ic (TPS2553 for example).
    And, what if main PCB power supply (for example +12V) will turned off? Current from USB connector (I suppose, 1A maximum) will power up whole PCB?
    Ok, but what if +5V stepdown converter will powered up from output to input? What if +5V current will flow to +12V net? There are some other loads (much more than 1A), with UVLO less than +5V. Probably I even will see more than +5V on +12V net, cause of inductor in +5V stepdown converter, and dynamic load on +12V net during startup.
    So, I want to understand: How can I protect OTG power net?
    I want to use OTG for software updating, and for testing.

  • #2
    So, I read datasheet on TPS2553 again, and find that ic block reverse current, so I don't need another protection for this net.
    Also, I add voltage supervisory ic to +12V net, and it block load enabling.

    But, I see iMX6 Rex Development Baseboard schematic, and there is no any voltage switch ic on OTG power net (just ferrite bead).


    • #3
      This is what we have on our OpenRex board. See the schematic (Page 28):

      Click image for larger version

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      • #4
        Robert, thank you!