what is the relation of transmission distance and Baud rate,for ADM2582E?

In my project, I want to transmit data in the 1Mbps Baud rate on RS485 bus, and the transmission distance will be up to 50 metres away. can ADM2582E finish the mission? 

  • 0
    •  Analog Employees 
    on Sep 5, 2012 6:34 PM over 7 years ago

    Hello panlinjie,

    Yes, the ADM2582E will transmit at 1 Mbps over 50 metres of cable. With this distance of cable, you do need to make sure that it's properly terminated at both ends, with a resistor value matching the cable impedance (typically 120 Ohm for RS-485).

    We have an RS-485 Implementation Guide application note, this explains various aspects of designing an RS-485 bus. The chart on page 5 for data rate vs. distance has about 50 metres at 1 Mbps. This is very conservative general guideline for RS-485. Typically RS-485 transceivers today, such as the ADM2582E, would transmit across longer distances, particularly with best practices in implementation.

    Best regards,

    Conal

  • dear Conal,

    thanks for your reply. I see the isolation DC/DC of ADM2582E will regulate the voltage to 3.3v.

    In my previous test, I find 5v power will transmit farther  than 3.3v power at the same data rate. So, I am very worried that ADM2582E will not transmit so far at so high speed.

    the following graph is your test for ADM2582E?

     

  • 0
    •  Analog Employees 
    on Sep 5, 2012 7:44 PM over 7 years ago

    Hello panlinjie,

    The graph above is from the RS-485 specification and provides a very conservative guideline. The actual maximum data rate is application-specific (cable type, jitter-tolerance, duty-cycle distortion specification, etc.) but will typically be very much above the line in that graph, including for the ADM2582E.

    Our 3.3V-powered transceivers are RS-485 compliant and adhere to the same minimum Vod specification (as 5V parts) on the driving node even with a fully loaded bus (32 unit loads). Please refer to the ADM2582E/87E datasheet for the driver test circuit, fig 24 on page 12.

    Regards,

    Conal

  • Conal,

    I am still a little worried.

    I would like to know whether VISOIN pin of ADM2582E can be powered 5v ?

    I know the above graph is  standard, but I would like to know whether ADI have tested the the relation of transmission distance and Baud rate,for ADM2582E?

    if the graph is for ADM2582E, I will believe it.

    best regards

    linjie pan

  • 0
    •  Analog Employees 
    on Sep 6, 2012 6:38 PM over 7 years ago

    Hello Linjie,

    The characterisation we have undertaken of typical performance of the ADM2582E is presented in the plots in the data sheet, these don't include transmission distance vs. data rate.

    We have checked some specific higher data rates and longer cable lengths in our lab for particular cases, this has confirmed that typical performance is beyond that shown in the graph above.

    The Visoin pin is only designed to be supplied from the Visoout pin, and does require a 3.3V supply.

    Best regards,

    Conal