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LMK05318: Unused output pins

Miranda Gu
Genius 14777 points
Part Number: LMK05318

Hi team,

My customers want to know how to configure the unused output pins. 

  • For unused differential outputs, customers should either float the pins if this channel disabled by registers, or terminate the pins if this channel active in registers. Customer's question is that how to terminate the output pins? Placing a 49.9ohm pull-down resistor? 
  • For unused single-ended outputs, like only using P channel, how to terminate the N channel? Placing a 49.9ohm pull-down resistor? 

Appreciate your answers, thanks a lot!

  • 0
    TI__Expert 6140 points

    Hello,

    I would recommend that in either case they just disable the channel via register - this shouldn't be prohibitive in anyway. It will also have power savings.

    If that can't be done - then AC coupled with 50 ohm to ground for N and P side for output types LVPECL, LVDS, CML.

    • I guess they could've programmed the channel to LVPECL but then only need one side of the channel - then that would make sense why they can't disable via register. In that scenario answer remains the same - N side can be terminated AC coupled with 50 ohm to ground and this way they avoid reflections causing bad performance on P side.

    Note that if they're using CMOS - they can program CMOS single ended and have the other side disabled not needing any termination. Programming the output channel to CMOS(+ / HiZ) or CMOS(- / HiZ) would achieve this. Similarly if they want N side active and P side disabled, they can choose (HiZ / +) or (HiZ / -).

    Thanks and regards,

    Amin