I have an MCU connected to a logic level P-FET(part no AO3401A). The source is wired to a 3.3V regulator that also feeds the MCU. The drain is wired to an LED and a header that connects to a second board with some LEDs and buttons. When I leave the header unplugged the circuit works as expected, and I'm able to turn the LED on and off from the microcontroller. However when I connect the second board the microcontroller browns out and resets continuously. I don't see any fluctuations on the +3.3 when looking at it with a scope.
Why exactly am I seeing these brownouts, and what might I do to prevent them?
Thanks! Circuit diagram below