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SN65LVCP408

Ulf Kristiansen
Prodigy 20 points
Other Parts Discussed in Thread: SN65LVCP408, SN65LVCP404

Hi.

On the SN65LVCP408 crosspoint switch there is a Vbb (biasing) pin. Should this be connected to 1.6 V only when using AC coupled inputs or should it always be connected to 1.6 V?

Best regards

Ulf Kristiansen

  • 0
    TI__Expert 7850 points

    Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4

    Hello Ulf,

     

    The Vbb pin can be left open as the device can self bias as noted in figure one page 4 of the data sheet .   The unused input pins can be left open but  for AC coupled case it is typically not good practice especially if the outputs are feeding a sensitive I/O for the system.

     

    Best Regards,

     

    Atul Patel

  • 0
    TI__Intellectual 1810 points

    Hi Ulf,

    VBB needs to be connected to 1.6V only in ac-coupled mode which is actually preferred for better jitter performance.

    Best regards.

    Hassan.

  • 0 in reply to Atul Patel
    Mastermind 6755 points

    Hello, I'm User

    > The unused input pins can be left open but  for AC coupled case it is typically not good practice especially if the outputs are feeding a sensitive I/O for the system.

    • Let me ask you a question by the disposal of unused input terminals.

      The opening of the input tells you not to be good by an AC couple, is it necessary to process what it is on an input terminal when I make input open?
  • 0 in reply to HA
    Prodigy 30 points

    This message seems to contradict the one above.  Message above states Vbb can be left open because it is internally generated.  The referenced figure in the datasheet actually has it connected to GND.  Your message states it should be connected to 1.6V.

    I have AC coupled inputs.  What should I do with the Vbb pin?

    I also have unused inputs.  What should be done with them?

    Thanks,

    Phil

  • 0 in reply to Phillips Smith
    Prodigy 30 points

    Update:

    For anyone looking for Vbb information, there is a more explicit statement about what to do with the Vbb pin in the SN65LVCP404 datasheet.  I still don't know what to do with the unused inputs.

  • 0 in reply to Phillips Smith
    TI__Mastermind 20820 points

    Hi All,

    If the SN65LVCP408 is DC coupled than the VBB pin can be used to drive a common mode voltage of other than 1.6V.

     

    If the SN65LVCP408 is AC coupled than the VBB pin can be left floating as the device is self biased to 1.6V.

     

    With any type of device like this (i.e. signal conditioner, buffer, cross point switch) it is never a good idea to leave the input pins floating, it is always a better idea to force them to a known state (i.e. VCC or GND) instead of letting them floating. This will limit the amount of noise you let into your system and give insight into what is happening on your outputs because you know what they are supposed to be.

    Regards,

    Mike