ADM2687

Hi.
Connecting as fig.46 datasheet, is it necessary bias resistor ?
If not , what do
i have in a momentary
transistion with all device in receving state? Is it
necessary a ground conection on the bus among the devices ? the total lenght of
bus (9 devices total) is
less 1 meter (very short). Also i don't think is
necessary the termination (500kb), isn't it ?Thanks.
Mario.

  • 0
    •  Analog Employees 
    on Mar 11, 2016 3:20 PM over 4 years ago

    Hi Mario,

    The ADM2687E has a fail-safe receiver input feature, which eliminates the need for bias resistors by specifying the receiver input threshold between −30 mV and −200 mV.
    The guaranteed negative threshold means that when the voltage between A and B decays to 0 V, the receiver output is guaranteed to be high.

    But, if you need added noise immunity in your system, then you can add biasing resistors.
    Please see AN-960 pages 6 and 7 for details.
    http://www.analog.com/media/en/technical-documentation/application-notes/AN-960.pdf

    Adding a ground 2 connection between multiple ADM2687E nodes is a customer decision, which is application dependent. For a very long bus cable a ground 2 cable connection may add to bus robustness in the face of high voltage transients. For a 1 meter bus length i don't think a Ground 2 connection is neccessary.

    For high data rates and longer cable lengths it is recommended that you add two termination resistors, each at the the opposite bus extreme ends.
    For your low data rate, short cable system you may not need termination, but in general it is recommended to use termination resistors as best practise.

    Best regards,
    Richard