Arduino Nano voltage regulator failure

There were a few reports of Arduino Nano boards getting somewhat damaged during assembly and testing of the avionics units.


The entire unit simply stopped working when powered via CAN-Bus. It is working fine when powered via USB.


The problem:

Arduino’s on-board voltage regulator AMS1117 becomes permanently damaged.


Root cause:

The reason why the AMS1117 becomes damaged is that the avionics unit gets connected to unpowered CAN-HUB while being powered via USB. For a very brief moment the output capacitor of the CAN-HUB board creates a short-circuit situation drawing reverse current through the AMS1117 until the capacitor is fully charged.
The datasheet for this voltage regulator recommends a protection diode connected between input and output in reverse to the current flow. If the input of the regulator is shorted, the diode will simply bypass the current around the regulator. For some reason Arduino nano does not have this diode.



Do not connect the unpowered CAN-Hub while the unit is powered via USB.
Apply the power to the unit from the CAN-Hub first. Then connect the USB if required.