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XTR110: XTR110 external transistor

Part Number: XTR110
Other Parts Discussed in Thread: OPA2350

Hi all,

I am using the XTR110 as 0-5V to 4-20ma wired according to the device datasheet, page 6, having the pin5 as input and pin 3 to GND.

I am using the VP0808L mosfet transistor and everything is running well.

When I change the transistor with the ZVP4525GTA, i get a damaged XTR110 immediately after power on the circuit.

Same if I use the FQT2P25TF.

Looking more carefully at the damaged units, having replaced the testing transistors with the trusted  VP0808L I measure 



which tells me that internal opamp A1 is damaged....

My RL=312Ohm, V(pin5)=2.5V and, Vcc=+22V

Any ideas for the cause of damage?

Any suggestions for an alternative transistor, having better power dissipation than the VP0808L?



  • Hi Nick,

    Thank you for your post. Can you share with me details on how you're testing these different transistors? Do you have two different layouts? I ask because the VP0808L transistor that you say works fine is offered in the TO-92 package, whereas the other two transistors are in the SOT-223 package. These two packages have different pin-outs and I want to make sure they are wired correctly first. 


  • Hi Tamara

    Thanks for your comments.

    Actually the PCB is designed for the SOT-223 transistors and because they were not available, I used the VP0808L.

    Once I got them and did the replace, I realized that they damage the XTR110.

    The connections are all correct as you can see in the board.

    I believe these transistors are not compatible with the XTR110.

    Any ideas?


  • Hi Nick,

    the XTR110 works very well with the VP0808L, usually. But it might need good cooling, especially if the output current is set to 40mA and a high voltage is dropping across the source drain channel.

    Also, have you read the section "INPUT VOLTAGE RANGE" on page 7 of datasheet? Are you sure that you haven't applied a negative going voltage to the input pins?

    And: Have you mounted a supply decoupling cap directly across the supply terminals of XTR110?

    Take a fresh XTR110 and a fresh VP0808L and try again.

  • Hi Nick,

    Kai is correct. You may need good cooling for the higher power transistors. See the following app report for more information:


  • Hi Kai.

    The problem occurs when I connect the SOT-223 transistors (ZVP4525GTA or FQT2P25TF). VP0808L works just fine!!!

    I don't use any negative voltages in my circuit, only +5V and rail-to-rail 5V opamps (OPA2350) The input (XTR110 pin 5 ) is driven by a 2.5V Voltage reference.

    There are decoupling caps, 10uF/35V TANT as suggested across CRT110 pin 16.

    Please note that the fault us happening immediately after power on the circuit. I'm sure because I monitor Vload at power on.




  • Hi Tamara,
    It should not be a heat issue, the damage happens too fast after power on. I see no excess current in my lab PSU. I monitor the current.
    And if this is the issue, why the TO-92 VP0808L survives?
  • Hi Nick,

    have you connected the two drain terminals of SOT-223 package to each other in the layout?

    Why are you using such small solder pads for the SOT-223 MOSFETs? These tiny solder pads cannot act as a heatsink.

    After the ZVP4525GTA and FQT2P25TF have destroyed the XTR110, are they also damaged? Or are they still ok afterwards?

    Is there any issue with the soldering of the SOT-223 packages? What shows the ohmmeter after soldering but before you power-on the board? Any unwanted short circuits?


  • Hi Nick,

    We haven't heard from you in a week. I hope Kai's comments have resolved the issue. I will close this thread.