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XTR110: Datasheet information.

Part Number: XTR110
Other Parts Discussed in Thread: OPA191

The data sheet for XTR110 has a FIGURE 10. 0A to 10A Output Voltage-to-Current Converter.

1) Shouldn't pin 10 be to Com? That pin is not shown.

2) if I want my input to be 0 to +5V, Pin 10 would go to Com and I would reverse pins 4 and 5? Thanks.

  • Hi Naser,

    You are correct, pin 10 should also be shown going to com in figure 10. For a 0 to +5V input, you should tie pins 9 and 10 to com and reverse pins 4 and 5 as you mentioned. You may also require a pot between pins 6 and 7 for zero offset adjustment.

    Zak Kaye
  • Hello Naser,

    1. Referencing the XTR110 datasheet Figure 1 table; to obtain a 20 mA span with a 0 to 10 V input pin 9, the 16 mA span set and pin 10, the 4 mA span set would both be grounded connecting R7 (6250 Ohms) and R8 (1562.5 Ohms) in parallel (1250 Ohms). With a 10 V input at pin 4, 2.5 V is developed across the 1250 ohms resulting in a current of 2 mA. This 2 mA flows through R8 developing a 1 V drop. The 1 V drop is them mirrored across REXT. Using the REXT equation on Pg. 8, REXT = R9 (span old / span new), REXT for a 0 to 10 Amp output equates to: REXT = 50 (20 mA / 10 A) = 100 milliohms. One volt across a 100 milliohm REXT equates to a current of 10 Amps for a 10 V input. Yes, pin 10 should be connected to Comm.
    2. Yes, reversing the connections for pins 4 and 5 and grounding pin 10 will set the XTR110 for a 0 to 10 Amp output, with a 0 to +5 V input.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • Thanks for both replies. What about pin 8. Should that be left open in the Figure 10 example?
    Also, do you have a modification example to Figure 10 where the current can be reversed with a relay, simplifying (in some cases) Figure 8.
  • Naser,

    Pin 8 should be left floating. Pin 8 is there to give you more flexibility with your span if you need to accommodate non-standard ranges.

    I do not believe you can use a relay to produce bidirectional current with the XTR110. The inner circuitry of the device is essentially a two-stage high-side V-I converter and can only source current. To be able to sink current, you have to add a low-side stage external to the XTR as in Figure 8.

    What exactly is your end goal? It is starting to sound like you may be better off using something like an improved howland current pump or some other V-I circuit. Can you share some more information about your application?

  • Hi Zak: He is looking to drive a servovalve with +/-50mA into a 40 inductive load. Range could be +/-55mA, but at least +/-50mA. His interface is to a micro controller. Please let me know. Thanks.
  • Naser,

    An XTR is not ideal for that application. I would suggest using an improved howland current pump with a device such as the OPA191, which has a max output current capability of +/-65mA. Please see the attached presentation for an analysis on the circuit including design equations:

    Improved Howland Current Pump.pptx


    Zak Kaye