use the microUSB or the J4.1 (5 volt DC in) and J4.9 (GND) pins. Never use both.
It is possible to supply power at 3.3 volt to the Arietta using:
Using this power option it is not possible to use the miniusb connector anymore.
To mantain the USB client function on the micro USB it is required to remove the R36 resistor as shown below. In this way the microUSB is not powering Arietta but the USB lines to the PC will work as usual.