## Overview of FST3245WM The **FST3245WM** is an 8-bit high-speed CMOS TTL-compatible bus switch. It is primarily used to connect or isolate two 8-bit buses with minimal propagation delay. It is commonly found in memory interleaving, bus isolation, and voltage translation applications. ### Key Specifications | Parameter | Specification | | :--- | :--- | | **Logic Family** | FST (Bus Switch) | | **Number of Bits** | 8-bit | | **Configuration** | Octal (8 channels) | | **Propagation Delay** | 0.25 ns (Maximum) | | **On-Resistance ($R_{on}$)** | 4 $\Omega$ (Typical) | | **Operating Voltage** | 4.0V to 5.5V | | **Package Type** | SOIC-20 (Wide Body) | | **Operating Temperature** | -40°C to +85°C | --- ### Internal Architecture and Pinout The device consists of eight high-speed N-channel MOSFETs that act as switches. When the switch is enabled, the connection is bi-directional. 1. **A1 - A8:** Port A Inputs/Outputs. 2. **B1 - B8:** Port B Inputs/Outputs. 3. **/OE (Output Enable):** The control pin. * **Low (L):** Connects Port A to Port B. * **High (H):** Disconnects Port A from Port B (High-Impedance state). ### Logic Truth Table | /OE Input | Internal Switch State | Function | | :---: | :---: | :--- | | **L** | A = B | Connect / Bus Switch On | | **H** | Disconnected | Isolate / High-Z | --- ### Features and Benefits * **Zero Propagation Delay:** Because it uses a simple NMOS switch rather than a buffer, it introduces virtually no delay (typically < 250ps). * **Low On-Resistance:** The low $R_{on}$ ensures minimal voltage drop across the switch. * **Hot-Plug Protection:** It allows for "live insertion" of boards without corrupting the data bus. * **Level Shifting:** Can be used for 5V to 3.3V translation when used with a series resistor or by limiting the supply voltage. ### Common Applications * **Bus Isolation:** Separating a CPU bus from peripheral components to reduce capacitive loading. * **Voltage Translation:** Interfacing 5V TTL logic with 3.3V CMOS logic. * **Memory Interleaving:** Switching between multiple memory banks quickly. ---