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TPD12S016: Prevent back drive current from reaching FPGA?

Matthew Hagerty
Prodigy 20 points
Part Number: TPD12S016
Other Parts Discussed in Thread: TPD12S521, TPD12S520

I am driving an HDMI source via an FPGA.  I am having a problem where the required TMDS pull-up resistors in the sink (monitor) are feeding current back into my FPGA when the FPGA is power off, but the monitor remains on.  This current is keeping my FPGA in a quasi-powered state.

It looks like the TPD12S016 might do what I want, but it is unclear to me if the chip will specifically prevent (provide a path for?) the current I have described above?  The datasheet indicates:

"Back-drive Protection on HDMI Connector Side Ports"

But does that mean the chip protects itself and will not provide a path for back-drive current, or does that mean it protect the signal lines from back-drive current as I need?

If is does not provide the kind of protection I need, is there a TI chip that does?

Thanks,

Matthew

  • 0
    TI__Mastermind 32651 points
    Matthew,

    The TPD12S016 will not ensure the the TMDS path resistors do not provide back power. It only will address the CEC, HPD, SCL, and SDA pins that it provides level shifting.

    The TPD12S016 is only providing ESD protection for the high speed lines. I am not aware of a chip that will provide reverse current protection for the high speed lines.

    Regards,
    Chuck
  • 0 in reply to Chuck Branch
    Prodigy 20 points
    Hello Chuck,

    While waiting for moderator approval on my post I did some more reading and digging around. It seems the TPD12S521 (for a source) and TPD12S520 (for a sink) provide the back-drive protection on all the HDMI pins. Unfortunately the 521 is only available in a TSSOP package which is too big for my design. The 520 will work for a transmitter and has a QFN package that would work for me, but since it is sink-specific, it does not provide the 5V supply+current-limit needed for a source.

    ON Semi also makes a chip that is the same as the 521, but it is also in the same package. Finally I found Nexperia (NXP) makes the same protection chip in a 4x4mm HXQFN, IP4786CZ32S. Since that fits my design and provides the 5V supply, I'll have to go with that over the TPD12S520. Is TI planning on producing the TPD12S521 in any different packages?

    Thanks,
    Matthew