## Overview of FST3245WMX The **FST3245WMX** is a high-performance CMOS 8-bit bus switch produced by ON Semiconductor (formerly Fairchild). It is primarily used for high-speed signal switching and voltage level shifting in digital circuits. --- ### Technical Specifications The following table outlines the key electrical and physical characteristics of the FST3245WMX: | Parameter | Specification | | :--- | :--- | | **Logic Family** | FST (Fast Switch Technology) | | **Configuration** | 8-Bit Bus Switch | | **Supply Voltage ($V_{CC}$)** | 4.0V to 5.5V | | **On-Resistance ($R_{on}$)** | 4Ω (Typical) | | **Propagation Delay** | < 0.25 ns | | **Package Type** | SOIC-20 (Wide) | | **Packing** | Tape & Reel (indicated by 'X') | | **Operating Temperature** | -40°C to +85°C | --- ### Key Features and Functionality 1. **Low On-Resistance:** The internal switches have extremely low resistance, which minimizes signal distortion and insertion loss. 2. **Zero Propagation Delay:** Because it acts as a mechanical-style switch rather than a logic buffer, it introduces virtually no delay in the signal path. 3. **OE (Output Enable) Control:** It features an active-low Output Enable (`/OE`) pin. When `/OE` is low, the A and B ports are connected; when high, the switch is in a high-impedance (Hi-Z) state. 4. **Voltage Level Translation:** When used with a diode in series with $V_{CC}$ or by reducing the supply voltage, it can effectively translate 5V signals down to 3.3V levels. --- ### Pin Configuration (SOIC-20) ```text +--U--+ /OE |1 20| VCC A1 |2 19| B1 A2 |3 18| B2 A3 |4 17| B3 A4 |5 16| B4 A5 |6 15| B5 A6 |7 14| B6 A7 |8 13| B7 A8 |9 12| B8 GND |10 11| NC (or GND) +-----+ ``` --- ### Common Applications * **Bus Isolation:** Isolating a microprocessor from a heavily loaded bus to improve signal integrity. * **Voltage Level Shifting:** Bridging 5V legacy systems with newer 3.3V components. * **Hot-Plugging:** Protecting circuitry during live insertion of cards or peripherals. * **Multiplexing:** Routing data between two different memory banks or I/O ports. ---