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current loop rx/tx isolation

MJ16032
Prodigy 240 points
Other Parts Discussed in Thread: RCV420

Hi There,

I am designing a current loop input/output controller.  I need to add isolation to the current loop input and current loop output.  I would like to get some recommendations on the best topology for this design as I have not designed for an industrial application before.

 

On the input I will be using something similar to the RCV420 current loop receiver and or building my own opamp signal processing to interface an ADC.  1) based on this information could you recommend the best means of isolation to the input of the processing components?

On the ouput I will use some digital isolators that will run to an ad7707 device that will drive the current loop on the output the isolators can be powered from the AD7707 up to 5mA.  2) can you recommend the most approprite isolation that might be used on the output side.

 

Attached is a basic flow diagram showing main components and isolation.

 

  • 0
    TI__Mastermind 28265 points

    Since you mentioned our RCV part I'm assuming you are using a 4-20mA current loop that requires the isolation of analog signals. It also requires the circuit supply current to be less than 3.5mA, particularly if you plan to send data via HART protocol.

    Our digital isolators however are, as the name implies, digital isolators which can distinguish only between high and low. hence they might be useless for your application unless you turn your analog current into a PWM voltage.

    The next best approach that comes to mind seems to be the use of opto-coupler isolation, such as shown in the apps section of the attached HCPL4200 data sheet.

    let us know how it will work out for your application.

    Regards, Thomas

    HCPL4200.pdf