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XTR111: XTR111

Larry Brick
Prodigy 250 points

Part Number: XTR111
Other Parts Discussed in Thread: AMC1300, , XTR115, AMC1301, ISO122, ISO124, ISO121, OPA333, OPA388

What would be the best part(s) to use for the following requirement?

Isolated 4-20mA current loop isolator, one 4-20mA input, four 4-20mA outputs all isolated from the input and all isolated from each other.

  • 0
    TI__Mastermind 23050 points
    Hey Larry,

    Do you need a 2-wire or 3-wire interface? Is every 4-20mA loop going to run off of its own loop supply then? If I've understood correctly then you already have a 4-20mA signal you need to interface with. One thing you could do would be to insert a shunt resistor into the loop and use 4 isolation amplifiers, like the AMC1300 or AMC1301, to generate an isolated voltage for each line. Then you could run each of those into an XTR to generate your loops. There are many devices that would work here, it just depends on what you need for your system. XTR111 is good for 3 wire applications, You could use an XTR115 if you need 2-wire.
  • 0 in reply to Zak Kaye
    Prodigy 250 points

    Hello Zak,

    Thank you for the information.  I believe what will work for me is the AMC1301 and the XTR111 since I have a 3-wire application.  I have one question regarding the input side of the AMC1301.  Since I will have 4 isolated channels, can I use one AMC1301 with a single shunt resistor and then make parallel connections of the signal from the shunt resistor (Vinn & Vinp) to drive the other 3 AMC1301's?  I don't want to run into loading problems.

  • 0 in reply to Larry Brick
    TI__Mastermind 23050 points

    Hey Larry,

    You can tie them all to the same shunt, but depending on the value of your shunt resistor there may be some slight loading effects. You will need to determine what you can tolerate. The AMC1301 has a differential input resistance of 22kOhms. So putting 4 together gives you a net resistance of 5.5kOhms. If you used a 10 Ohm resistor to translate 20mA to 200mV, then this does cause a slight shift in your shunt resistance. Another effect to consider is the bias currents of each amplifier will flow through that resistance and create slightly more error, but since your shunt resistance will be small this effect should also be pretty negligible.

    One detail I overlooked is that all of the analog isolation amplifiers in our portfolio have fully differential outputs, except for the ISO121, ISO122, and ISO124 family. This means you would also need an INA or diff amp to perform a differential to single ended conversion.

    Another approach would be to use an analog opto-isolator like the HCNR200 in the configuration shown below:

    Here you need 4 of these circuits in your input loop so you have to make sure you have enough compliance headroom for all of the devices. For low voltage dc precision you could use something like the OPA388 or OPA333.

  • 0 in reply to Zak Kaye
    TI__Genius 11135 points
    Larry

    We haven't heard back from you so we assume this answered your questions. If you need more help just post another reply below.

    Thanks
    Dennis