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DS34C86T: Interface with 3.3V FPGA and ability to turn off 5V supply

Part Number: DS34C86T

Hi all

I need to interface a 5V RS422 receiver (like DS34C86T) to a 3.3V FPGA. Moreover I need the ability to turn

off the 5 volt supply while the 3.3 volt supply remain on.

I think to connect the DS34C86T output to a 74LVC1G125 (powered at 3.3 volt) input and the 74LVC1G125 output connected

to the FPGA.

My question is: 

If I turn off and on the 5 volt supply, but the 3.3 volt is always on, can some current flow through the pins damages the DS34C86T or the 74LCV1G125 or the FPGA?

If yes, are there circuit solutions to protect from this problem?

Thanks for help

  • Rossi,
    I don't think either unpowered RS422 or level shifter will be damaged by a 3.3V voltage. If you want to limit the current flowing back to 5V devices, you can refer to this post that links to a document that shows how to add a blocking diode.

    e2e.ti.com/.../678278

    Please let me know if you have any more questions.
    Regards,
    Hao