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TLK110: TLK110 MDIO will not initialize

Alexei Shkurko79
Prodigy 20 points
Part Number: TLK110

on power up TLK110 will not respond to host via MDIO. Traced it down to JTAG_TRST pin. We have 2.2K pullup but about 30% of boards from current build fail Ethernet test. The only way I can get part to work is to tie JTAG_TRST low or remove external pull-up.  Can we have JTAG_TRST pin on TLK110 permanently tied LOW or should it be left floating? Data sheet has no info on how JTAG_TRST should be used. I found couple similar posts on e2e forums but they all went to offline conversations without solution been posted so everyone can see it.

  • 0
    TI__Mastermind 19780 points
    Hi Alexei,

    It is not ideal to tie JTAG_TRST low. I assume you are powering up without a reference clock present to the TLK110. Is this true?

    Best Regards,
  • 0 in reply to Rob Rodrigues
    Prodigy 20 points

    Hi Rob,

    reference clock for PHY supplied by external 50Mhz oscillator which is powered by same 3.3V rail as PHY. since oscillator has some startup time it it will not be running at the time PHY is powered. I believe data sheet has no specifics if clock shall be applied before power is applied. in our design after power is applied we toggle RESET line (~200mS low pulse) before MDIO configurations applied.  after removing external pull-up from failed board they stated working. The question now is should we tie together RESET and JTAG_TRST so we have guarantied reset of JTAG logic if we can't have JTAG_TRST tied low?

    Best Regards,

    Alexei