Peripheral USB on STM32 MCUs app note from STMicroelectronics. Link here (PDF)
STM32 microcontrollers include a group of products embedding a USB (Universal Serial Bus) peripheral. Full-speed and high-speed operations are provided through embedded and/or external PHYs (physical layers of the open system interconnection model).
This application note gives an overview of the USB peripherals implemented on STM32 MCUs, and provides hardware guidelines for PCB design, to ensure electrical compliance with the USB standards.