XTR111 SET Pin damaged

Hello Abhijit,

Are you physically changing the Rset resistor while power is applied to the XTR111?  Doing so could cause unexpected results. 8V on a 250Ohm load would indicate output current levels around 32mA.  The output current limit of the XTR111 is typically closer to 42mA, is there something else in the circuit limiting the output current?

Also, can you share a schematic and PCB layout so we can verify your basic connections?

Hello Collin 

Thanks for replying.

The Rset Resistor is fixed and not changed while power is applied.

I am working with a general purpose board (pcb tracks with solder metal)

Pl find my schematic attached.

I had 2 nos of XTR111 , the first one got its SET pin damaged due to unknown reasons.

The second was populated and it could never control the current as per Rset or Vin.

It is fixed at 12mA.

Not sure whats happening.

EDIT : 500 ohms across C4 is not populated on BoardTransmitter.pdf

Hello Abhijit,

Thanks for attaching your schematic.  The connections look appropriate and you have good power supply decoupling.  How much current are you sourcing from the VREG circuit?  I noticed you're using an external BJT to increase the output current. 

Both the MSOP-8 (DGK) and DFN-10 (DRC) packages of the XTR111 require the PowerPAD on the bottom of the IC to be properly soldered to a PCB landing pad that is electrically connected to GND.  This is discussed near the end of the XTR111 datasheet.  I can't tell based on your description of your PCB if you're providing a proper PowerPAD connection or not.

Hi Collin

Thanks for responding

I was not loading the Vref at all.

The schematic shows that.

I know the power pad should be soldered,but currently I am evaluating this,and this is going to be part of a bigger system.

The only current drawn was signal current.

Thanks for the additional information. Without the PowerPAD properly soldered to GND the device may not function properly. Even if you're not using a PCB with the recommended land pattern, try to connect the PowerPAD to GND on a new device and see if it functions properly.

Thanks again
Although if you read my original post,it did work the first time without the power pad not connected to ground

Dear Collin

As per your advice i have made a new board for the XTR111, with a PowerPad.

I populated the XTR111 and its Pad soldered to ground.

I observe the same behaviour.

Vin = 2.83V

RSET = 10k 

Iout = 9.83 mA

RSET changed to 5k Iout is unchanged

Am i doing something wrong here?

Hi Collin
I changed the RSET to 2k5
Now i do get a variation at Iout
But it is from 9.28mA to 11.8mA , for corresponding voltage of 1v to 2.5v , above 2.5v, Iout remains unchanged.
I hope you can help me on this

Hello Collins
I forgot to mention that it works quite good with the BSP170 MOSFET.
Thanks for the support

Thank you for sharing your results with the community Abhijit, glad it's working now.