I have a very size- and power-constrained application for the STM32F7 series. It will not make use of USB peripherals. Is it possible to tie VDDUSB to GND and eliminate the recommended bypass caps to save space, or do I need to supply it with either VDD or an external supply and bypass it? The block diagram makes it look independent from the other systems. The reference manual only states that one of the supplies is required for the USB transceivers.