I want to konw voltage stability of 3.3V, but there is no details in official docment. i need the voltage to power a sensor

my program goto busfault handler, but I do not know the reason

my board is nucleo64 f401re. I used DMA and Idle interrupt to receive data of uncertain length. it works when baudrate is 115200. but it receives up to 16 bytes under baudrate 921600, other bytes has been losed. I want to higher speed, how to fixed t...