I’ve found great difficulty to find an application note of this USB soundcard on a chip. I ve decided to share here the info that I’ve found. I’ve made various PCB’s with this chip on it without any trouble so it’s very reliable. NOTE: USB series and pull-up resistors R1/R2 of 22ohm and R3 of 1.5Kohm are absolutely needed. YOU MUST INSERT THIS RESISTORS OR THE CIRCUIT WON’T WORK. L1 and L2 and C3/C4 are not so important, in fact the circuit will work without them but I suggest to be included in your design for EMI filtering.
For example my PMT adapter use this chip in order to sample PMT pulses and connect to PC. Theremino MCA in fact uses the audio codec chip as hi-speed/hi-quality ADC
CM108AH this is the original datasheet
USB-FOB This USB Radio interface uses a CM108AH and there is a full schematic!