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FSA221

USB2.0 High-Speed (480Mbps) and Audio Switches with Negative Signal Capability

Fairchild Semiconductor 

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 3M) 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

USB 2.0

Source

Audio

CODEC

Vaudio

D+

R

D-

L

Switch Select

Control Circuitry

Vbus

ASel

Rpd

GND

D+/R

D-/L

5V

Vbus

ID

USB

Mini -AB

Connector

Figure 5. Typical Application

GND

© 2006 Fairchild Semiconductor Corporation

FSA221 • Rev. 1.1.0

3

www.fairchildsemi.com

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