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LMH1219: Unused IN1+/- pin connection

K. Sasaki14
Guru 10200 points
Part Number: LMH1219


Please let me know unused IN1+/- pin connection.

I'm understanding unused IN1+/- pin should be connected to GND through 4.7uF and 50ohm. Is this understand correct?

Now our customer is connecting unused IN1+/- pin to GND through 0.1uF capacitor. However they cannnot redesign.

Do you have any concern about this connection?

 Best Regards,
Kohei Sasaki

  • 0
    TI__Guru* 93570 points
    Greetings Sasaki-San,

    This should be fine and there is no concern.

    LMH1219 selects either IN0 or IN1 based on IN_OUT_Sel pin settings. As long as this pin is either high or float, IN0 is selected.

    Regards,,,nasser
  • 0 in reply to Nasser Mohammadi
    Guru 10200 points
    Nasser-san,

    Thank you for your prompt reply.
    Is recommended connection to GND through 4.7uF and 50ohm?


    Best Regards,
    Kohei Sasaki
  • 0 in reply to K. Sasaki14
    TI__Guru* 93570 points
    Hi Sasaki-San,

    Either way is fine. I mean you can use either 4.7uF and 50-ohm R or leave IN1 un-connected. Each one has it's own benefit. With 50-Ohm and 4.7uF capacitor un-used input is terminated correctly. On the other hand, we should be careful about any cross coupling or cross talk with traces going to these two components.

    Regards,,nasser
  • 0 in reply to Nasser Mohammadi
    Guru 10200 points
    Nasser-san,

    Could you tell me careful point when unused IN1 is left open if you have?
    I think leave IN1 open is better if there is no concern especially because we can reduce components number.


    Best Regards,
    Kohei Sasaki
  • 0 in reply to K. Sasaki14
    TI__Guru* 93570 points

    Hi Sasaki-San,

    Leaving IN1 open is better. But, if customer already has connections to IN1 this should not cause a problem.

    Regards,,,Nasser

  • 0 in reply to Nasser Mohammadi
    Guru 10200 points

    Nasser-san,


    Thank you for your reply.
    Which connection pattern is the best? Please let me know your opinion.

    - GND connection through 4.7uF and 50ohm.
      This is terminated correctly. However we have to care noise coupling to traces going to these components. And this connection increases external components.

    - GND connection through the capacitor like 0.1uF or 4.7uF etc...
      This is simple AC coupling. Same as above, we have to care noise coupling. However external components number is lower than 4.7uF and 50ohm termination.

    - leave open
      I think this is the most simple. However I think input pins become the most high impedance condition more than the above two, and we have to care noise coupling especially.

    Best Regards,
    Kohei Sasaki

  • 0 in reply to K. Sasaki14
    TI__Guru* 93570 points
    Hi Sasaki-San,

    Proper termination through 4.7-uF Cap and 50-Ohm R with a very short trace is the best option.

    Regards,,nasser