I made a prototype board of data acquisition and powered it like in the schematic below:
This is a simplified schematic.
There is a USB port that provides power for the whole board; a FT230 for the USB-UART conversion; a ST6600 for smart button functionality; a LDO-3.3V to power the microcontroller (PIC32MZ).
When I press the button, the ST6600 assert the signal that enables the LDO-3.3V and so the microcontroller.
But here I have a little trouble: if I plug the USB cable and NOT press the button, the LED on the output of microcontroller turns on feebly. So I noticed that the problem is due to the RX and TX signals which from the FT230 are connected to the microcontroller. These signals go to 3.3V when the USB is plugged and, even if the microcontroller is off, there is a current that flows inside it and goes out on the output of the LED; I can even read a 1.8V on the 3.3V net of the circuit.
Is this a normal behaviour (maybe I made mistake with this schematic) and if so, can anyone explain me why of the output current and the 1.8V?