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XTR111: Mosfet for XTR111

Part Number: XTR111


I've done a design with XTR111 and i've seen it needs a mosfet(BSP170P L6327) that is recommended for it, but i can't use it because i haven´t got space to put it. could you advice me one smaller?

Thanks for all,

  • Hi Gonzalo,

    see table 1 of datasheet.

    Keep in mind that the PMOSFET has to dissipate a lot of heat when the output is short-circuited to ground. With a 24V supply about 24V x 20mA = 0.48W has to be dissipated. Because of this you will not only need a robust PMOSFET but also sufficient copper on the printed circuit board to remove the heat.


  • HI Gonzalo,

    The dominant portion of power dissipation for the current output is in the external FET.  As Kai has explained, it is important to consider the power dissipated by the external FET, which is a function of the power supply voltage, and current output range.    

    Please include the appropriate heatsink for the FET in the design.  For example, the XTR111-2EVM incorporates the ZXMP6A13FTA P-Channer MOSFET on the SOT23-3 package. If you refer to the XTR111 board layout on page 7 of the XTR111EVM User's Guide, the drain of the P-FET (pin2, pin4 heat sink) are connected to an isolated copper fill on Top and connected to another isolated copper fill on the bottom for heat dissipation.

    Thank you and Best Regards,


  • Hi Gonzalo,

    The external P-FET will dissipate less power when used in a lower supply application.  For example, if your supply is at +10V, and the maximum current is 20mA, the power dissipated in the FET would be limited to about ~0.2W. 

    - Please clarify the supply voltage range requirement on this XTR111 3-wire transmitter application?  

    - What is the maximum current range that needs to be supported?

    - Kindly let me know what is the maximum load resistance required in this application.  If possible, please provide an schematic of the XTR111 circuit.

    Keep in mind, when reducing the XTR111 voltage supply, the XTR111 requires a minimum compliance voltage.  The XTR111 by itself, without accounting for the minimum external P-FET transistor source-to-drain voltage, the compliance range is 2V below the supply voltage Vvsp. In addition, foot note (4) on page 3 states the XTR111 minimum compliance voltage is limited by (+Vvsp-2V) + VDS, where VDS is the external transistor drain-to-source voltage required for linear operation of the external P-FET transistor.  We also need to account for any series resistances in the output path, voltage drops due to external diodes/clamps on the current path.  See figure below.

    Thank you and Kind Regards,


  • Hi Gonzalo,

    I have not heard back from you, I will close this query for now. However, if you have additional questions, please let us know.  

    Thank you and Regards,