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LSF0102: Support MDC need pull-up resistor or not

Alan Chang
Intellectual 2260 points
Part Number: LSF0102
Other Parts Discussed in Thread: TXS0102

All,

On LSF0102 datasheet, it showed need Rpu for MDIO and MDC.
But actually, we know MDC doesn't need the pull-up resistor.
1. Does it mean we need to add a pull-up resistor for MDC if we would like to use LSF0102 as MDIO Level Translator ?
2. Or we also don't need a pull-up resistor for MDC if we would like to use LSF0102 as MDIO Level Translator ?

  which one is correct?

  • 0
    TI__Guru 59750 points
    Hi Alan,

    I know that the MDIO is an open drain interface which means that the output side would need a pullup resistor to define a valid logic level.
    Hence, while using the LSF you would have both input and output pullup resistor to work with MDIO interface.

    Instead of this, i would encourage to consider using the TXS0102 device which has the internal 10k pullup resistor saving BOM cost and space on the board.
  • 0 in reply to ShreyasRao
    TI__Intellectual 2260 points

    Hi Shreyas,

         My question is if customer uses MDC, does it need pull-up resistor? from MDC spec., pull-up resistor seems not need, but LSF0102 need it or not in MDC application? 

      

  • 0 in reply to Alan Chang
    TI__Guru 59750 points
    MDC is unidirectional and push pull - > Input side of the LSF doesnt need pullup resistor. Output side will need pullup resistor.
    MDIO is bidirectional and open drain.-> Both input and output side needs pullup resistors on LSF
    TXS0102 can support both without the need for pullup resistor on either input or output side.