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XTR106U current transmitter

Stan Long
Prodigy 20 points

Other Parts Discussed in Thread: XTR106

We are using the TI circuit that is shown in the TI datasheet. This circuit was used some time ago very successfully. Right now,  the XTR106 has no 5V on Pin 14 and no 5.1V on the 5V Reg out pin. We installed a TI sample XTR106pa only on a board and 15V was connected to pins 10 and 6 and still no 5V. What is happening especially with the circuit? The circuit will indicate 4ma but when the sensor is pressured to 125psi the 4ma remains. Does the PN2222A  enter into it? Mouser supplied the original parts.

  • 0
    TI__Guru 64775 points

    Hi Stan,

    The XTR106 is a pretty tried-and-true product and so I'm not sure what is causing the lack of proper operation that you're experiencing.  Can you clarify whether you're debugging recent field failures on an existing product or if you're designing a new product and are having trouble?  

    After re-reading your post I think there's a chance that this is a simple test method issue regarding some of the special considerations that must be applied to 2-wire 4-20 mA transmitters such as the XTR106.  The XTR106 should be powered between pins 10 and 7 (V+ and IOUT).  The IRET pin (pin 6) is the local return for any circuitry powered from VREG, VREF2.5, or VREF5, but should not be treated as a "system GND" or improper operation will ensue.  This is because the IRET pin must effectively float in relation to the IOUT pin.  This is required because as the output current (IOUT) changes in the loop, the voltage on the IOUT pin will change as well because of the changing current that flows through the loop-supply sense resistor (V = I * R).    This creates some interesting challenges when evaluating a 2-wire transmitter on the bench because any instruments connected to the loop-powered side (between VREG, VREF2.5/5, and IRET) must float in relation to any instruments used to power/monitor the main loop-supply applied to the system (between +V and IOUT).  The best way to accomplish this is the use of handheld, battery powered meters to measure the voltages on the loop-powered side.  Just be sure not to connect the negative input of the handheld meters to the loop-supply GND or you'll defeat the idea of "floating" these input meters.

    In short, the 2222 should be fine and I believe this is a simple connection issue with your testing.  Connect your loop supply between +V and IOUT and then measure the VREG, VREF2.5, and VREF5 voltages using a floating meter placed between the voltage of interest and IRET.  If that does not fix the issue then I'll next be asking for a schematic and PCB layout to review your design for any accidental errors.