Analog Angle Article

Analog switches handle both audio, USB sources

The FSA201 (USB 1.1; 12 Mbps) and similar FSA221 (USB 2.0; 480 Mbps) multimedia-oriented, analog double-pole double-throw (DPDT) switches from Fairchild Semiconductor are designed to pass both single-polarity USB signals as well as bipolar analog audio signals. The tiny switches are targeted at compact handheld and battery-powered applications, “where a single I/O connector's pins must fulfill multiple roles,” noted Richard Lewis, Analog Signal Path Marketing Manager.

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The switches incorporate automatic Vbus detection to find the USB signal when an USB application is plugged in. Bandwidth (-3 dB) is at least 720 MHz for the FSA221 and 250 MHz for the FSA201.The 8-lead devices can swing negative to -2.0V, and so are well-suited to supporting the greatly reduced clicks and pops of bipolar Class D amplifiers (compared to single-supply, non-zero-volt biased designs); this operation also eliminates the need for a dc-blocking capacitor. They have low on-resistance Ron of 3 Ω for reduced current consumption, longer battery life, and enhanced audio performance.

The FSA221 is available in an ultra-thin molded leadless package (UMLP) that is 1.4 x 1.8 x 0.55 mm high; both devices are also available in a slightly larger 1.6 x 2.1 mm MicroPak. Despite the small size, the switches provide 10 kV of ESD protection, especially important where the IC may be located extremely close to the connector and outside world. The FSA201 is $1.10 (click here for data sheet) while the FSA221 is $1.25 (click here), in 1000-piece lots.

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