Texas Instruments SN74S240DW

Overview

SN74S240DW from Texas Instruments is an octal inverting buffer/line driver with 3-state outputs, designed for memory address and bus driving applications. It features dual 4-bit channels, PNP inputs reducing DC loading, 400-mV noise margin, and maximum propagation delay of 7 ns at 5 V. It drives terminated lines down to 133 Ω and supports mixed 3.3-V/5-V logic interfacing.

For engineers reviewing the SN74S240DW datasheet, SN74S240DW pinout, SN74S240DW application, or SN74S240DW equivalent, key selection criteria include 3-state output control timing (tPZH/tPZL), high-current drive capability (64 mA sink), input hysteresis for noise immunity, and SOIC-20 package thermal performance (RθJA = 90.3°C/W).

Technical Context

The SN74S240DW implements Schottky transistor logic (S-TTL) with two independent 4-bit inverting buffers, each controlled by a dedicated active-low output-enable (G) input. Its PNP input structure reduces bus loading while built-in hysteresis improves noise margins on all inputs.

It operates over 0°C to 70°C with VCC = 4.75–5.25 V, delivers 64 mA low-level output current, and achieves 4.5–7 ns typical propagation delay under RL = 90 Ω / CL = 50 pF conditions - optimized for high-speed bus termination and memory address buffering.

Key Specifications

Pinout & Package

SN74S240DW is housed in a 20-pin SOIC (DW) package measuring 12.80 mm × 7.50 mm, with standard 0.050″ lead pitch and gull-wing leads for surface-mount assembly.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal inverting buffer applications.

Compared with SN74LS240DW and SN74ALS240N, SN74S240DW delivers 2× faster propagation, 2.7× higher sink current, and SOIC packaging for better thermal management - making it optimal for high-density, high-speed bus buffering where signal integrity and drive strength are critical.

Availability

SN74S240DW is available at Aetrix Electronics and suitable for memory address buffering, server backplane interfaces, LED display row driving, and industrial I/O expander applications requiring stable component supply and long-term industrial availability.

Supply support for SN74S240DW includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor company specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74S240DW belongs to TI's legacy S-TTL logic family, engineered specifically for high-speed bus driving, memory address buffering, and noise-immune signal restoration in commercial-grade systems.

FAQ

What is the maximum operating temperature for SN74S240DW?

The SN74S240DW is rated for commercial operation from 0°C to +70°C ambient temperature. This range is defined in the Recommended Operating Conditions table and applies to all electrical specifications including propagation delay, output drive, and noise margin. Exceeding +70°C may cause parameter drift or reliability degradation; thermal design must ensure junction temperature remains within absolute maximum limits.

Does SN74S240DW support mixed-voltage interfacing?

Yes, SN74S240DW inputs tolerate down to 2 V and are compatible with both 3.3-V and 5-V logic families. Its VIH threshold is 2 V (min), and VIL is 0.8 V (max), allowing direct connection to 3.3-V microcontrollers without level shifters. However, output voltage levels remain TTL-compatible (VOH ≈ 2.4–2.7 V, VOL ≤ 0.55 V), so downstream receivers must accept TTL input thresholds.

How does the 3-state output control work on SN74S240DW?

SN74S240DW has two independent active-low output-enable inputs: Pin 1 (1G) controls Channel 1 outputs (1Y1–1Y4), and Pin 19 (2G) controls Channel 2 outputs (2Y1–2Y4). When either G pin is LOW, its corresponding Y outputs follow the inverted A-input states; when HIGH, those outputs enter high-impedance (Hi-Z) mode. This allows dynamic bus sharing without external gating logic.

What is the purpose of input hysteresis in SN74S240DW?

Input hysteresis (0.2–0.4 V) in SN74S240DW raises the effective VIH threshold when transitioning from LOW to HIGH and lowers the effective VIL threshold when transitioning from HIGH to LOW. This prevents oscillation or metastability on slow-rising signals - such as those from long PCB traces, mechanical switches, or unterminated cables - thereby improving noise immunity without external Schmitt triggers.

Can SN74S240DW drive 50-Ω transmission lines?

No, SN74S240DW is specified to drive terminated lines down to 133 Ω, not 50 Ω. Driving 50-Ω loads would exceed its 64 mA IOL rating and risk overheating or parameter violation. For 50-Ω systems, use purpose-built line drivers like SN65LVDS31 or SN75ALS197. SN74S240DW is intended for medium-impedance buses (e.g., memory address, control backplanes) where 133-Ω termination matches its drive strength.