XIAO SAMD21 Burning Up with Adafruit LiPo BFF


Connecting the Adafruit LiPo BFF to the XIAO SAMD21 trying to add a battery recharge circuit to a project.

I was burning up XIAOs and was trying to figure out why. Upon looking at the unit itself, it does not appear the protection diode from the VUSB (5V Line) is not present on the XIAO as seen in the schematic and the board.

Is this an error that has been addressed? Ie, are there units that do have this protection diode?

The 5V from the Adafruit BFF runs back into the XIAO and it’s likely the USB Voltage plus the LiPo voltage is what is causing them to burn out. I have 20 or so XIAOs ready to go, but I don’t know if I will be able to use them with this project if the protection diode is not there to prevent over-voltage.

The Adafruit Lipo BFF only has 3 active lines. 5V, Ground, and a voltage divider to look at the status of the battery. XIAO is hooked up 5V to 5V line, Gnd to Gnd (with a switch for power), and I run the voltage divider to an input pin.

I’d rather use the XIAO over the QtPy due to the external crystal - but if there is no intention of using this protection diode as seen in the schematic, I’m not sure I will be able to.


There is a diode in the schematic, but it is not actually mounted. You can see it by checking the terminals of the USB connector with a multimeter. The following post is helpful.
Board Supplied 3.3v Power vs USB - #3 by Match-san

If the diode is not mounted, the schematics should clearly mention it.

Use NM not mounted or NP not populated.

Otherwise, the schematics are useless.