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xtr116 problem

karan patel1
Expert 1085 points
Other Parts Discussed in Thread: XTR116

in my circuit i am using two xtr 116 to generate 2 4-20ma.from that from one xtr116 i use voltage to power up my controller and other circuit and second one is only for 4-20ma generation.as in second xtr i am not using its voltage i unconnected its iret pin and only join 200k resistor between pin 1 & 2. so there should be 2ma current in that loop.but in multimeter 4.5ma current is showing. i made directly pcb so here i attach rough schematic drawn  on paper .i don know what is the problem

the out put of voltage follower ic for second xtr116(in which facing proble is 0v)so only 200k resister is in picture

  • TI__Guru 64295 points

    Hi Karan,

    Thanks for sharing your schematic, I have a pretty good idea of what you're trying to create.  However, this circuit will not operate as you've designed it because circuitry that interfaces with the input of an XTR116 device must be powered solely between the V+ and IRET pins of the XTR.  This is discussed in Parts 2, 4, and 5 of a 2-wire transmitter blog series we published recently (see link at bottom). 

    In short, for this system to work you'll have to use a digital isolator (ISO7310) to send the PWM signal from the MCU (which is powered by the 1st transmitter) to the 2nd transmitter.  This will isolate the two transmitters from each other as explained in the blogs. You'll need split the dual-channel op amp into two single channel op amps, each powered between the VREG/IRET supply of the XTR they are driving. 

    So the first transmitter will power the LDO, MCU, op amp, and 1/2 digital isolator.  The 2nd transmitter will power the other 1/2 of the digital isolator and the other op amp which drives the input to the 2nd XTR116.   

    Let me know if this is clear.

     https://e2e.ti.com/tags/4_2D00_20mA%2btransmitter