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Problem in adjusting zero & span in XTR110

Mohammad Ashoori
Prodigy 50 points
Other Parts Discussed in Thread: XTR110

Hi everybody

I'm using XTR110 to provide 4-20 mA current from 0-10V Voltage.

with the data available in data sheet i could not get the ideal current.

in 0v i have 8mA and zero adjust haas a low range.

but in 10 V every thing is OK and i have 20 mA and span has a good range.

note: I am using IRF9520n p-ch MOSFET

using +10v Reference

using two 100k Multi turn for zero and span

using a 12V zener diode,from Gate to Source

using a 20k resistor between pin 12 and 2 according to figure 3 in the datasheet

using 1uf tantalium capacitance for power supply filter

Important: I have an accidental short connection between pin 6 and 8.does it make any damages???

help me,please

  • Prodigy 50 points

    in the recent experiment the ranges of current was 8-26 mA
    I think i should change my Mosfet.
    How can we find out that the XTR110 is not damaged?

  • in reply to Mohammad Ashoori
    TI__Guru 62915 points
    Hi Mohammad,

    I suggest ordering a new XTR110 device and before you apply power verify that all of the connections are appropriate. We don't have any information on possible damage caused by accidentally shorting the internal op amp offset trim and span trim pins together.
  • in reply to Collin Wells
    Prodigy 50 points

    Thank You Collin
    Can i decrease the output current by increasing "Rspan" ?

    according to this:

  • in reply to Mohammad Ashoori
    TI__Guru 62915 points
    Hello Mohammad,

    Yes, for a new and fully operational (not damaged) XTR110 this would work. However, as mentioned above if you've damaged the XTR110 device in your system, or still have pins 6 and 8 shorted together, we have no information on how the device will behave.
  • in reply to Collin Wells
    Prodigy 50 points
    Ok,I will use another XTR110,but now i have another question!

    I couldn't find the recommended Transistor and i used IRF9520N instead.
    with this p-ch mosfet ,the current was 9-27 mA
    i changed my P-ch Mosfet and i used IRF9540.
    with the second one ,the current was above 70mA.

    What's Your idea about it?
    can i reach to ideal current by using recommended Transistor??

    the maximum current of drain (Id-max) :
    IRF9520N-------> 6.8 A
    IRF9540 --------->19A
    IRF9513(recomended)---------> 3A
  • in reply to Mohammad Ashoori
    TI__Guru 62915 points
    Hi Mohammad,

    Are you connecting the PMOS correctly? Remember the current flows from the source to the drain of the PMOS device. Make sure you have the gate, source, and drain connected properly. Also, until you get an XTR110 device that hasn't possibly been damaged and you've removed the short between pins 6-8 the output current likely won't be correct regardless of the selected PMOS.
  • in reply to Collin Wells
    Prodigy 50 points

    Hi Collin,

    Yes,i know these basic rules well.

    so you say the output current should be 4-20 regardless of the selected PMOS ?!

    in the last experiment i added 680 Ohm to pin 9 and output current was 7-20 mA.
    This is better than previous results but still there is a big difference.
    I checked several method and now i think i should change XTR110 with new one.

    Isn't there any way to reduce 7mA (output current as zero) to 4mA? if there is not ,buying the new IC is the first and the last choice.

    Thank you for your helps