Arduino Micro Hardware Issue - T1 Maximum Gate-Source Voltage Violation

[twomeyw2]

As I understand on the Arduino Micro, MOSFET T1 acts as the "5V selector". If Vin is present, it turns off the MOSFET to isolate the Vin generated 5V rail from the USB 5V rail. I looked at the datasheet for the FDN340P MOSFET and it specifies an Absolute Maximum Gate-Source voltage of +/-8V. When the board is first connected to a power supply the T1 Source voltage will be 0V, so anything over 8V could be stressing the part. Even after the 5V regulator ramps on, the T1 Source will be 5V, allowing for a maximum Vin of 5+8 or 13V. The Arduino Micro webpage specifies a maximum input of 20V.

In addition to violating the maximum Gate-Source voltage specification, tying a MOSFET Gate directly to the input voltage rail raises some reliability concerns given MOSFET susceptibility to ESD damage.

I think in the short term, the Arduino Micro webpage should be updated to specify 7V input voltage. A long term solution could be to add a resistor and zener diode to the T1 gate circuit to prevent over-voltage conditions and offer some protection at the Gate or specify a MOSFET source that has a larger maximum Gate-Source voltage.

http://arduino.cc/en/uploads/Main/arduino-micro-schematic.pdf