+3.3V External Power Supply

[ASieg]

Hello, I would like to use an external supply (3.3V) for my nucleo. the user manual tells me that I have to connect PIN 12 (IOREF) to +3.3V and also the PIN 16 to +3.3V. Both pins from CN7. Is this correct?

And also GND to external GND. I already removed the 0 Ohm resistors from SB2 and SB12.

What does the PIN IOREF do? What happens when this pin is floating?

Best,

Alexander