## Overview of the FSUSB22QSC The **FSUSB22QSC** is a high-speed, low-power USB 2.0 switch produced by ON Semiconductor (formerly Fairchild). It is designed to allow a single USB port to switch between two different USB devices or controllers. --- ### 1. Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Switch Type** | 2:1 Mux/Demux (Double-Pole, Double-Throw) | | **Interface Standard** | USB 2.0 (High Speed, Full Speed, Low Speed) | | **Operating Voltage ($V_{CC}$)** | 3.0V to 3.6V | | **Bandwidth** | 750 MHz | | **On Resistance ($R_{ON}$)** | 6.5 $\Omega$ (Typical) | | **Package Type** | QSC20 (Quarter Size Outline Package) | --- ### 2. Functional Description The device acts as a high-speed analog switch. It is transparent to the USB data stream due to its high bandwidth and low capacitance. * **D+/D- Routing:** It routes the differential data signals (D+ and D-) from one common port to one of two selected ports. * **Selection Control:** A digital input pin (**S**) determines which path is active. * **Enable Pin ($\overline{OE}$):** An Output Enable pin allows the user to disconnect all paths (High-Z state) to save power or isolate the bus. --- ### 3. Pin Configuration (Common QSC20 Pins) The following table highlights the critical pins for integration: | Pin Name | Type | Description | | :--- | :--- | :--- | | **$V_{CC}$** | Power | Supply Voltage (3.3V typical) | | **GND** | Power | Ground | | **S** | Input | Select Input (Low = Port 1, High = Port 2) | | **$\overline{OE}$** | Input | Output Enable (Active Low) | | **$D+/D-$** | I/O | Common USB Data Pins | | **$nD+/nD-$** | I/O | Switched USB Data Pins (where n is 1 or 2) | --- ### 4. Typical Applications * **Mobile Handsets:** Switching a Micro-USB port between a PC data connection and a dock/accessory. * **Laptops:** Routing internal USB signals to different modules (e.g., Wi-Fi or Bluetooth cards). * **Embedded Systems:** Sharing a single USB controller between two different sensors or peripherals. --- ### 5. Implementation Considerations When designing a PCB with the FSUSB22QSC, keep these factors in mind: 1. **Impedance Matching:** Maintain 90 $\Omega$ differential impedance for D+/D- traces. 2. **Decoupling:** Use a 0.1 $\mu$F ceramic capacitor as close to the $V_{CC}$ pin as possible. 3. **ESD Protection:** While the chip has internal ESD protection, additional external diodes are often recommended for user-facing ports.