UCC28704: FET is burned

Hi Seongwoong, 

Thanks for reaching out! Can you check/provide the power ratings of the resistors that are burnt? At first look, I would recommend putting the two current sense resistors in parallel (R89 and R137) to have current be distributed among them so the resistors have less stress, but there may be more to debug this issue. 

Can you provide the power ratings of the passive components? 

the size of the resistor 3216 is 0.5W 

after power on, the resistors are not burnt.

If all of the boards are burnt, that's right.  The resistors burnt occurred on a few boards after several months

another reason..?

Thanks

Regards,

Nick.

I think the possibility : 28704 is operated abnormally due to the 256303 ?

Hi Seongwoong,

I am assuming that it is the burnt FET that leads to other resistors to fail. Can you check the FET's drain voltage and source voltage at full load to see if it is operating correctly? 

Thanks, 

Claire

Hi Claire,

Gate dampling resistor is 47 ohms. Is it fine? 

I think the resistor is big?

Thanks,

Nick

Hi Seongwoong,

The series gate resistor functions for reducing ringing and control turn on time for FET.

The following app note provides details on the choice of gate drive resistor.

https://www.infineon.com/dgdl/Infineon-EiceDRIVER-Gate_resistor_for_power_devices-ApplicationNotes-v01_00-EN.pdf?fileId=5546d462518ffd8501523ee694b74f18

I think 47-Ohm resistor should be fine. If the FET turns out to switch faster than you would like, increase the resistor value (less current flows in the gate to charge the FET). If the FET switches slower than you would like, decrease the resistor value (10-Ohm) for more current flowing into gate.