© 2007 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FSA321

• Rev.1.0.6

3

Functional Description

The FSA321 is a combined USB and audio switch that

enables sharing the D+/D- lines of a USB connector with

stereo audio CODEC outputs. The USB Sel pin has an

internal pull-down resistor that results in a default audio-

mode configuration. The switch can be configured for

USB Sel pin. The audio switch path also handles

negative signals, eliminating the need for large coupling

capacitors and greatly reducing the potential for audio

pop. Termination resistors on the audio R and L ports

are enabled when the switch is in USB mode, this also

helps reduce audio pop when enabling the audio path.

The FSA321 allows for an audio override state by

forcing A/LP Sel high when USB Sel is high. This is

useful for USB car kit applications or if the device is in a

cradle charger

when “Send/End” is pressed.

Application Diagram

USB 2.0

Hi-Speed

Controller

Audio

CODEC

FSA321

D+

D-

R

L

D+/R

D-/L

USB Sel

0.1µF

Figure 3. Typical Application Diagram