ADM2485 - Transient Immunity and Line Biasing

Dear Sir,

We are manufacturer of range of actuators which uses RS485 communication as backbone.

Currently we are using TI,  ISO3088 - isolated RS485 converter.

We are revisiting the design and want to have ADM2485 to be tried and if found satisfactory, it will replace RS485 converter in all our designs.

Our unit is housed in metallic IP68 casing in open environment.

These units are installed in very harsh conditions like thermal power plant, oil rigs and oil loading and unloading terminals (not petrol stations).

Find attached present schematic we are using.

We are observing harsh transient disturbance, let me know information about ADM2485 for this scenario.

Also, please let me know how ADM2485 handles line biasing and termination requirement.


Shrivardhan BS Rao

  • 0
    •  Analog Employees 
    on Oct 4, 2016 7:37 AM

    Hi Shrivardhan BS Rao,

    What harsh transient disturbances are you referring to? Do you need to meet particular specifications using the ADM2485 as the RS-485 interface? If yes, then please provide details...

    The ADM2485 isolation barrier provides immunity against electrical disturbances, for example:

    ADM2485 data sheet, table 1, provides a common mode transient immunity specification of 25 kV/us min.

    For RS-485 termination recommendations, please refer to our application note AN-960, page 5.

    An RS-485 bus typically is terminated with two resistors, one at each furthest end of the bus. The termination resistance equals the characteristic impedance of the cable, most cables fall within the 100 to 150 ohm range.

    For RS-485 failsafe / biasing recommendations, please refer to our application note AN-960, page 6.

    The ADM2485 includes an integrated fail-safe feature:

    The receiver input includes a fail-safe feature that guarantees a Logic high RxD output when the A and B inputs are floating or open-circuited.

    Best regards,


  • 0
    •  Analog Employees 
    on Aug 2, 2018 3:36 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

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