## Technical Overview of FST3245QSC The **FST3245QSC** is a high-performance, 8-bit, low-resistance bus switch manufactured by Fairchild Semiconductor (now part of ON Semiconductor). It is designed to provide high-speed switching and level translation between different voltage nodes. --- ### 1. Key Technical Specifications | Parameter | Specification | | :--- | :--- | | **Logic Family** | FST (Bus Switch) | | **Number of Bits** | 8-Bit (Octal) | | **Supply Voltage (Vcc)** | 4.0V to 5.5V | | **On-State Resistance (Ron)** | ~4Ω (Typical) | | **Propagation Delay** | 0.25ns (Maximum) | | **Package Type** | QSOP-20 (Quarter Size Outline Package) | | **Operating Temperature** | -40°C to +85°C | --- ### 2. Functional Description The device consists of eight high-speed N-channel MOSFET switches organized in a single block. * **Switching Mechanism:** When the Output Enable (`/OE`) pin is **Low**, the switches are closed, connecting the A-port to the B-port. When `/OE` is **High**, the ports are in a high-impedance (Hi-Z) state. * **Zero Propagation Delay:** Unlike standard logic buffers, the FST3245 acts as a wire when closed. It does not regenerate the signal, meaning it adds virtually zero timing skew. * **Level Translation:** Because it is an N-Channel switch, it can be used for voltage translation (e.g., converting 5V signals to 3.3V levels) when a diode or specific biasing is used on the Vcc line. --- ### 3. Pin Configuration (QSOP-20) | Pin No. | Name | Function | | :--- | :--- | :--- | | 1 | /OE | Output Enable (Active Low) | | 2-9 | A0 - A7 | Port A Inputs/Outputs | | 10 | GND | Ground | | 11-18 | B7 - B0 | Port B Inputs/Outputs | | 19 | NC | No Connect | | 20 | Vcc | Power Supply | --- ### 4. Typical Applications * **Bus Isolation:** Isolating a CPU from a heavily loaded bus to improve signal integrity. * **Hot-Swapping:** Protecting sensitive circuitry during "live" insertion of cards. * **Voltage Translation:** Interfacing 5V legacy components with 3.3V modern controllers. * **Memory Interleaving:** Routing data lines between different memory banks. --- ### 5. Truth Table ```markdown | /OE Input | A-Port / B-Port State | | :---: | :---: | | L | A = B (Connected) | | H | Z (Disconnected/High-Z) | ```