## FSUSB74: High-Speed USB 2.0 4-Port Switch The **FSUSB74** is a high-performance, bi-directional, low-power USB 2.0 switch manufactured by ON Semiconductor (formerly Fairchild). It is designed to multiplex four USB channels into one common D+/D- pair. --- ### 1. Key Technical Specifications | Parameter | Specification | | :--- | :--- | | **Function** | 4-to-1 USB 2.0 Switch | | **Operating Voltage ($V_{CC}$)** | 2.4V to 4.4V | | **Bandwidth (-3dB)** | 800 MHz | | **On Resistance ($R_{ON}$)** | 6.5 $\Omega$ (Typical) | | **Operating Current** | < 1 $\mu$A (Ultra-low power) | | **Package Options** | 16-Lead UMLP / DQFN | --- ### 2. Core Functional Blocks 1. **Analog Switches:** High-speed MOSFET-based switches that maintain signal integrity for USB 2.0 High-Speed (480 Mbps) data rates. 2. **Control Logic:** A 2-bit selection interface ($S_0$, $S_1$) and an Enable ($\overline{OE}$) pin to manage routing. 3. **ESD Protection:** Built-in protection to handle electrostatic discharge up to 12kV (HBM) on certain pins, critical for external connectors. --- ### 3. Pin Configuration and Truth Table The device uses a binary selection method to route the Common (D+/D-) pins to one of the four ports (H1, H2, H3, or H4). | $\overline{OE}$ | $S_1$ | $S_0$ | Function | | :---: | :---: | :---: | :--- | | HIGH | X | X | Disconnect (High-Z) | | LOW | 0 | 0 | Path 1: Common to H1 | | LOW | 0 | 1 | Path 2: Common to H2 | | LOW | 1 | 0 | Path 3: Common to H3 | | LOW | 1 | 1 | Path 4: Common to H4 | --- ### 4. Circuit Design Considerations * **Impedance Matching:** The FSUSB74 is designed to minimize capacitive loading ($C_{ON} \approx 6.5 pF$), which is vital to passing the USB 2.0 "Eye Pattern" test. * **Power Rail:** Since it is often used in mobile devices, it can be powered directly from a Li-ion battery (up to 4.4V). * **Level Shifting:** The control pins ($S_0, S_1, \overline{OE}$) are compatible with low-voltage GPIOs (1.8V logic), even if $V_{CC}$ is higher. --- ### 5. Common Applications * **Mobile Handsets:** Routing a single Micro-USB/USB-C port to internal components like a baseband processor, application processor, or an FM transmitter. * **Tablets/Laptops:** Switching between multiple internal USB peripherals. * **Docking Stations:** Managing data flow from multiple inputs to a single output.