• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 48 subscribers
  • Views 2232 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

XTR112 current generator trouble.

Matias Nabarro
Prodigy 20 points
Other Parts Discussed in Thread: XTR112

Hello. I'm in trouble with a XTR112. I inteded to use it as a variable current generator for simulating a 4-20mA sensor.

It works quite good, except in the near 4 mA zone. I can't get it to regulate smoothly between 4 to 7 mA zone, it changes abruptly from 4.1 to 5.2 mA.

My zone of interest is from 4 to 12 mA.

Any clue ? attached is an image of my implementation. I feed 12VDC in X1. In J3 I have a LED and in J1 I have a 5K linear potentiometer. 

Thanks in advance.

Matias, from  Neuquén - Argentina 

  • 0
    Genius 5430 points

    Matias;

    I suspect that you are violating the XTR112 common mode voltage range-- check the data sheet specifications and circuit diagrams. I do not see Rcm in your circuit diagram.

  • 0 in reply to Neil Albaugh
    TI__Mastermind 27715 points

    Matias,

    Neil is correct. Place a resistor between Vin- and Iret in order to keep the common-mode input voltage within the correct range of 1.25V to 3.5 V.

    The XTR112 data sheet recommends an Rcm = 3.3k, but for your configuration 2.1k might be a better choice. This biases Vin- at 1.5V, which gives you a 2V input span to work with. In either case, only about half of the potentiometer's range will be useful - once the wiper gets past ~50% the voltage at Vin+ will exceed 3.5V.

    To get your 4-12mA with a 2V input span, set your Rg potentiometer to 50% so that the XTR112 sees a resistance of 10k.

    Best regards,

    Ian Williams
    Linear Applications Engineer
    High Performance Linear

  • 0 in reply to Ian Williams
    Prodigy 20 points

    Thanks to both of you. I will try this evening. Then, I'll let you know if it worked ok.

    Best Regards. 

     

    PS: It worked OK with 1K5.

    Thanks again!.