Functional Description
The FSA221 is a combined USB and audio switch that
enables sharing the D+/D- lines of a USB connector with
stereo audio CODEC outputs. The switch is optimized
for high-speed USB signals and includes an automatic
Vbus-detection circuit. When a USB connector, rather
than a headphone, is connected to the ultra-portable
device the switch is automatically configured for high-
speed USB data transfer. If no Vbus is detected, and yet
VAUDIO is present, the switch is configured for the low-
distortion audio switch path. The audio switch path also
handles negative signals (down to -2V), which
eliminates the need for large coupling capacitors.
For those applications where the Vbus is generated as a
self-powered device or where Vbus is not removed, the
ASel pin provides the ability to switch, under software
control, to the audio path. The ASel pin is internally
terminated by a resistor to GND (typical value 3MΩ) and
requires no connection for the standard ultra-portable
(cell-phone, MP3, or portable media player). In an
application where the supply to the FSA221 Vbus pin is
not guaranteed to be removed, a GPIO pin can be used
to switch out of high-speed USB mode into audio mode,
using the ASel pin.
The FSA221 Vbus pin must be connected directly to Vbus
or a supply > 3.8V, not an LDO regulated down to 3.6V
or a Vbat-generated supply that may fall below 3.8V in
normal operation.
Application Diagram
3.0V– 3.6V
FUSS-BU2S.0B
Source
Audio
CODEC
Vbus
Vaudio
D+
R
D-
L
Switch Select
Control Circuitry
ASel
Rpd
GND D+/R
D-/L
FSA201
5V
Vbus
ID
USB
Mini-AB
Connector
GND
Figure 5. FSA221 Typical Application Diagram
© 2006 Fairchild Semiconductor Corporation
FSA221 Rev. 1.0.3
3
www.fairchildsemi.com