Hello,
I tried to use the FemToBuck (ref number COM-13716) with a Bluno Beetle BLE board (https://wiki.dfrobot.com/Bluno_Beetle_SKU_DFR0339) and a LED (https://www.lumitronix.com/en_gb/cree-x … 68466.html). I use a potentiometer as an analog input to the board (I tested it separately and it works great). Look at the schematic attached. Then, I use a digital pin of the board to output a PWM signal to feed the FemtoBuck. You can see the characteristics of the PWM signal on the screenshot attached. It worked great about 1-2 minutes then the FemtoBuck fried… You can see the fried trace at the bottom of the FemtoBuck on the picture attached.
If you have an idea of what I did wrong, please feel free to tell me 
There’s too much solder on your header pins and it looks like you have a short circuit between DGND and VIN. Having a short in that spot is going to draw a significant amount of current through one of the traces on the back of the board causing it to burn up.
Thank you for your reply.
I don’t know why I made these giant blobs but it is not the issue. I double checked the continuity and there is no short.
The only thing I see which can cause the issue is the voltage and frequency of my PWM signal. I measured with my oscilloscope a minimum voltage of -370mV and a maximum of 477mV (847mV peak to peak) and a frequency of 977Hz. The FemtoBuck is rated for a PWM signal which must oscillate between less than 0.4V to more than 2.4V, which is not the case here.
Obviously, I have an issue with my oscilloscope (I checked it with a known voltage source). The frequency is right but not the voltages. So, I still do not understand why my FemtoBuck fried.
I made a mistake with my oscilloscope. The PWM voltage is ok (0-5V) and the frequency is 980Hz. However, the output voltage of the FemtoBuck is only 2,8V while the power supply is 8V. The LED I’m using is a CREE XP-L V5. Its forward voltage is 2,95V (at 1A). I do not understand why I’m measuring such a low voltage at the output of the FemtoBuck.
