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XTR111: MOSFET Heating Issue

Dheeraj yadav
Intellectual 640 points

Part Number: XTR111

When i powered up my device the output is correct but after powered up the device mosfet start heating and continuously increases.

Attached schematic of the design, 

MOSFET Used - BSP170

BJT Used - 863-SMMBT2907ALT3G 

  • 0 in reply to Dheeraj yadav
    TI__Guru 55466 points

    HI Dheeraj,

    - Can you please let us know that the input voltage or DACOUT voltage is when the issue occurs and the resistor load at IOUT?

    Also, if the voltage regulator output is not used, please ensure to conect REGF and REGS together and bypass/ install a 2.2nF capacitor to GND.

    Thank you and Regards,

    Luis

  • 0 in reply to Luis Chioye
    Intellectual 640 points

    DACOUT Voltage in range of 0.1 to 3 Volts and load resistor is 15 Ohm, but yes regulator voltage pin is not in used and open .

  • 0 in reply to Dheeraj yadav
    TI__Guru 55466 points

    Hi Dheeraj,

    Are both Q2 and Q4 exhibiting the heating issue?  What is the part number of BJT Q1 and Q3?

    If you wish, we could review your PCB layout, please provide the Gerber files.

    As I have mentioned, per the datasheet recommendation, REG_F and REG_S must be connected together and bypassed with a 2.2nF capacitor when the regulator is not used.  It is not recommended to leave REG_F and REF_S disconnected.  Please refer to page 18 and Figure 45 of the datasheet.

     Thank you and Regards,

    Luis

  • 0 in reply to Luis Chioye
    Intellectual 640 points

    Yes sir both Q2 and Q4 exhibiting the heating issue.

    BJT Q1 and Q3 - 863-SMMBT2907ALT3G 

    Attached Gerber file and schematic 

    Manufacturing_Files_ConverterModule_I2c_V1.2.zip

  • 0 in reply to Dheeraj yadav
    TI__Guru 55466 points

    Hi Dheeraj,

    From the schematic perspective, the recommendations are as follows:

    - If the voltage regulator is not used, please short the XTR111 U4 and U2, REG_F and REF_S, and connect to a 470nF bypass capacitor to GND.   This will avoid potential issues with the internal regulator amplifier being open loop/unstable.

    - It is recommended to add protection circuitry such as transient voltage suppressor (TVS) diodes at the drain of Q4/Q2 (IOUT external connection).  For an example, please refer to the XTR111 Evaluation Module User's Guide.

    From the board layout perspective, the recommendations are as follows:

    I reviewed the layout as well, the BSP61 heatsink could be improved on the board layout.  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.

    Also, electrically, you could improve the layout by using independent vias on the XTR111 GND connections.  For example, the XTR111 pin 9, 10, and power pad all connect together and share one via to GND together with the C4 bypass capacitor.  A suggestion is to placing a via to GND on the power pad of the XTR111.

    Thank you and Best Regards,

    Luis