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ISO3086 biasing

Trevor Moorcroft
Prodigy 40 points
Other Parts Discussed in Thread: ISO3086

Does the ISO3086 transceiver require biasing on the Rx input?

  • 0
    TI__Genius 14015 points

    Hi Trevor,

    The R pin is actually an output pin. The D pin is the input data pin. Neither require biasing, as they are CMOS (not open-drain). Does that answer your question?

    Thanks,
    Jason Blackman 

  • 0 in reply to Jason Blackman
    Prodigy 40 points

    Hi Jason

    I meant on the receive differential inputs A and B as the datasheet refers to it as having a failsafe receiver

    Regards

    Trevor

  • 0 in reply to Trevor Moorcroft
    TI__Genius 14015 points

    Hi Trevor,

    It depends on your application, but under normal circumstances failsafe resistors are not required on the A and B lines.

    What the datasheet is referring to about the failsafe receiver is that the receiver threshold values are intentionally biased to be negative. Normally with RS-485, -200mV and below is a low while +200mV and above is a high. That case requires failsafe resistors to ensure that the receiver is in a known state during open, short, and idle conditions where the differential voltage is normally 0mV. 

    The ISO3086 (and many of our other transceivers) will be in a known state when there is greater than -10mV between A and B. That covers open, short, and idle. If your system is very noisy, then additional failsafe resistors may be required because you can't be sure where the receiver is going to transition in between -10mV and -200mV. 

    Does this help to explain the functionality?

    Thanks,
    Jason Blackman