The application note released by Keil explains the required steps to create a USB data logger application on an Infineon XMC4500 Relax Kit board.
The tutorial shows how to implement a data logger application that collects information from A/D channels and digital I/O ports, recording the data into files inside a micro SD card.
When connected to a computer itís enumerated as an USB Composite Device, allowing the access to the files and the transmission of a command to start/stop recording.

Application Note and Example Code are available on the Keil website:
http://www.keil.com/appnotes/docs/apnt_273.asp