You might be interested in checking the latest Silicon Laboratories documentation:

Silicon Labs  > Products  > Interface  > USB to UART (USB to UART Bridge)
  http://www.silabs.com/products/interface/usbtouart/Pages/default.aspx

Silicon Labs  > Products  > MCUs  > USB to UART Bridge VCP Drivers (CP210x USB to UART Bridge VCP Drivers)
  http://www.silabs.com/products/mcu/Pages/USBtoUARTBridgeVCPDrivers.aspx