FTDI Raspberry Pi Hub
The RPi USB Hub Module utilises an USB-to-UART/MPSSE IC, along with a GL850G USB hub controller IC. It provides engineers with up to 4 downstream USB 2.0 Hi-Speed (480Mbit/s) ports. Asynchronous serial data transfer rates from 300 bits/s to 12 Mbits/s at 3.3 V TTL levels are supported, while synchronous serial data rates of up to 30 Mbits/s can be dealt with on JTAG, SPI and I2C interfaces.
Application note AN_221_Adding_An_ADC_to_a_Raspberry_Pi explains how to install FTDI D2xx drivers on the Rapsberry Pi platform and then wire up an ADC to the RPi_HUB module.