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XTR110: Offset adjustment

ttd
Mastermind 7990 points
Part Number: XTR110

Dear Technical Support Team,

My configuration of XTR110KU  is following.

Vin: 0V～10V

Iout: 0mA～20mA

I adjust the offset pin(Volume register).Then almostdevice show 0mA(target is under 4.8μA) when Vin=0V after adjusting register(VR) of offset adjust pin(OK device).

However some device doesn't shows under 4.8μA in spite of adjusting offset pin(VR). It shows 5.6μA or 7.6μA or 8.0μA(NG device).

When replace the other device, it behave OK. It seems Individual difference of device.

I attached my schematic. Why is there difference between OK and NG?

XTR110KU_ver1.pptx

Best Regards,

ttd

  • 0
    Mastermind 7990 points

    Dear Technical Support Team,

    I updated attached file. Just added register part number.
    Could you see "XTR110KU_ver1.pptx" at previous my post.

    I guess that this problem is caused by MOSFET(leak current?).

    Could you advice appropriate MOSFET and adjustment for Vin=0-10V and Iout=0-20mA?

    Best Regards,
    ttd

  • 0 in reply to ttd
    TI__Genius 10850 points

    Hi ttd,

    Thank you for your post. When performing the offset (zero) adjustment, are you following the recommended procedure described on page 7-8 of the datasheet labeled "OFFSET (ZERO) ADJUSTMENT"?  Since you are using the device in the 0mA-20mA output range, in this case it is required to follow a special procedure, and set the input to a small nonzero value and then perform the adjustment of the R1 potentiometer to the proper output current result.  

    After performing this correction, when the input is zero the output will be zero.  The procedure is also described on Figure 7:

    -Tamara Alani

  • 0 in reply to ttd
    Guru 140200 points
    Hi TTD,

    yes, this can have to do with the unavoidable zero gate voltage drain current of MOSFET. Nevertheless, even with an ideal MOSFET it's rather unrealistic to expect a zero current of 0µA for this sort of voltage to current converter. Assuming a 500R burden resistance, giving a signal of 0...10V with an output current of 0...20mA, 5µA gives an error of only 2.5mV, which is 0.025% of full scale...

    Kai
  • 0 in reply to ttd
    TI__Genius 10850 points
    Hi ttd,

    I hope we were able to answer your question / resolve this issue. I am going to close this thread now. If you have any more questions, feel free to reply to re-open.

    -Tamara Alani