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XTR110: XTR110 external transistor

user3608438
Prodigy 40 points
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 

V(pin1)=V(pin13)=V(pin14)=Vcc=+22V

V(pin10)=0

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?

Thanks

Nick 

  • 0
    TI__Genius 10850 points

    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. 

    -Tamara

  • 0 in reply to Tamara M Alani
    Prodigy 40 points

    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?

    Nick

  • 0 in reply to user3608438
    Guru 140200 points
    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.

    Kai
  • 0 in reply to kai klaas69
    TI__Genius 10850 points

    Hi Nick,

    Kai is correct. You may need good cooling for the higher power transistors. See the following app report for more information: http://www.ti.com/lit/an/snva036b/snva036b.pdf

    -Tamara

  • 0 in reply to kai klaas69
    Prodigy 40 points

    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.

    Thanks

    Nick

      

  • 0 in reply to Tamara M Alani
    Prodigy 40 points
    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?
    Thanks
    Nick
  • 0 in reply to user3608438
    Guru 140200 points

    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?

    Kai

  • 0
    TI__Genius 10850 points
    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.