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XTR110 voltage divider input changes output

Other Parts Discussed in Thread: XTR110

Hee guys, 

I need some help with a project i'm working on. I have a XTR110 with a voltage divider connected to the input. The input voltage is 0-40V, the voltage divider converts this in to 0-10V (33k // 11k resistors(metal-film 2W 1%)). I use the simple schematic out of the data sheet (IRF9510 MOSFET) and 24V voltage supply. 

The voltage divider works perfectly and the XTR110 work perfectly(with an input from 0-10V) but when i connect those 2 together, the output current changes. With 0-10V input, the output is 4-20 mA. With the voltage divider in front of the circuit, the output become 4-16mA. (input voltage still 0-10V from the divider)

When 1 measure the voltage from the voltage divider at 40V input -> 10V. When i connect it to the XTR110, the voltage divider drops to 7.7V. Is this because the XTR110 uses current from its input somehow? 

I changed 1 resistor, so now it is 33K // 20K and the output current is 4-21 mA. But it still makes no sense to me. 

Can someone help me?


  • Hi Robert,

    If you look at the internal schematic of the XTR110 shown on the front page of the datasheet you'll notice that there's an internal resistor based voltage scaling network.  Resistors R3 and R4 will be directly in parallel with your external voltage divider resistors, affecting their value.  The other resistors inside the XTR110 are also in series/parallel with your external resistor divider.  I would suggest using an external unity-gain buffer to drive the input of the XTR110 after the voltage divider.  These effects can be seen using the unofficial XTR110 SPICE model I've included below.


  • Colin Wells,

    Thanks you very much for your fast responds! I've tried changing the resistors from metal-film to carbon film, and the problem was solved! (output 4,00-20,16 mA) I also tried your idea with the unity-gain buffer, it gave me an output from 4,00 to 20,06mA. So i'm going to use your idea.
    Thanks again!

  • Nice work Robert.  Did you change the resistor values as well when you switched to carbon film resistors? 

    The unity-gain buffer is our recommended solution because the low-output impedance of the buffer can easily drive the input impedance of the XTR110.