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DS160PR410: Unused channel termination, output state, AC coupling cap location

Taketo Sato
Genius 9915 points
Part Number: DS160PR410

Hello team,

I would like to know how we should handle unused channel(RX1P/RX1N) of DS160PR410 and found below post.
https://e2e.ti.com/support/interface-group/interface/f/interface-forum/988031/ds160pr410-unused-differential-input-output

I have below questions. Could you please give me comments?

  1. DS160PR410 is set with RXDET=L3 (50 ohm). Is AC coupling cap + 50 ohm to GND termination still valid regardless of the setting?
  2. Can I think that output(TX1P/TX1N) state will fix and not fluctuate or oscillation with the input termination?
  3. RX1P/RX1N pins are located next to VDD pin and the pin recommends placing caps close to the pin. In that case, can an AC coupling cap and resistor keep some distance from RX1P/RX1N?

Best regards,

  • +1
    TI__Guru* 93570 points

    Greetings Sato-San,

    1). Yes. This is a good design practice. The main purpose is to reduce any chance of noise coupling into un-terminated inputs. It is possible we may not see any issue even without these R&C termination but this is a good design practice and this provides a more robust design. 

    2). Since these inputs are AC coupled, we cannot say 100% it eliminates fluctuation. To further reduce negative side effects, suggestion is to have 50-ohm impedance controlled traces to these AC coupling Caps and 49.9-ohm Resistor terminations.

    3). Yes it can be some distance away. 

    Regards, Nasser

  • 0 in reply to Nasser Mohammadi
    TI__Genius 9915 points

    Hello Nasser-san,

    Thank you for the comments.

    Nasser Mohammadi said:
    Since these inputs are AC coupled, we cannot say 100% it eliminates fluctuation.

    Is there any other good way to fix output state on unused channel(TX1P/TX1N)?

    • RX0P/RX0N : used channel
    • RX1P/RX1N : unused channel <-- to have 50-ohm impedance controlled traces to these AC coupling Caps and 49.9-ohm Resistor terminations is best way to eliminate output fluctuation as much as possible?
    • RX2P/RX2N : unused channel <-- Set the channel PWDWN
    • RX3P/RX3N : unused channel <-- Set the channel PWDWN

    Best regards,

  • +1 in reply to Taketo Sato
    TI__Guru* 93570 points

    Hi Sato-San,

    The best way is to have 50-ohm controlled impedance long with R(49.9ohm)&C(220nF).

    Regards, Nasser