Texas Instruments SN74S240DWR

Overview

SN74S240DWR from Texas Instruments is an octal inverting buffer/line driver with dual 4-bit groups and independent 3-state output-enable (G) inputs, designed for memory address bus driving, clock distribution, and terminated line interfacing. It delivers 64 mA low-level output drive, 15 ns maximum propagation delay at 5 V, and operates across 0°C to 70°C. It is used in server memory subsystems to isolate and strengthen address signals between CPU and DRAM modules.

For engineers reviewing the SN74S240DWR datasheet, SN74S240DWR pinout, SN74S240DWR application, or SN74S240DWR equivalent, key selection criteria include its Schottky TTL-compatible input thresholds (VIH = 2 V, VIL = 0.8 V), high-current 3-state outputs capable of driving 133-Ω terminated lines, PNP-input architecture reducing DC bus loading, and hysteresis-enhanced noise immunity on all inputs.

Technical Context

The SN74S240DWR implements two independent 4-bit inverting buffer sections, each with active-low output-enable control (1G and 2G/2G). Its Schottky transistor logic (S-TTL) architecture enables faster switching than LS variants, with typical tPLH/tPHL of 7 ns under 90 Ω/50 pF load conditions.

Each input features built-in hysteresis (0.2–0.4 V) and PNP-based structure, minimizing input current draw (IIL = –400 µA per A input) and improving noise margins. Outputs are fully 3-state compatible, supporting bidirectional bus arbitration when paired with complementary devices like SN74S241.

Key Specifications

Pinout & Package

SN74S240DWR is housed in a 20-pin SOIC (DW) package measuring 12.80 mm × 7.50 mm, optimized for surface-mount reliability and thermal dissipation in dense PCB layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS240DWR and SN74ALS240N, the SN74S240DWR provides superior drive strength and speed for demanding memory and telecom interfaces, but consumes significantly more supply current-making it optimal where signal integrity outweighs power efficiency.

Availability

SN74S240DWR is available at Aetrix Electronics and suitable for server memory subsystems, telecom infrastructure equipment, industrial I/O expanders, and high-reliability embedded controllers requiring stable component supply across extended production lifecycles.

Supply support for SN74S240DWR 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 leader specializing in analog, embedded processing, and logic solutions, with decades of heritage in TTL and advanced logic families.

The SN74S240DWR belongs to TI's legacy S-TTL logic portfolio, engineered specifically for high-speed, high-drive bus buffering in memory, computing, and communications systems where signal fidelity and termination compatibility are critical.

FAQ

What is the maximum operating temperature range for the SN74S240DWR?

The SN74S240DWR is rated for commercial operation from 0°C to +70°C. This range is specified in the Recommended Operating Conditions table of the official datasheet (SDLS144D, Section 6.3). Operation outside this range may result in parametric deviation or functional failure. The device is not characterized for extended temperature grades such as industrial (–40°C to +85°C) or automotive.

Does the SN74S240DWR support 3.3-V logic inputs?

Yes, the SN74S240DWR accepts 3.3-V logic inputs reliably. Its VIH specification is 2 V minimum, and VIL is 0.8 V maximum at VCC = 5 V, making it compatible with standard 3.3-V CMOS/TTL output levels. This allows direct interfacing with 3.3-V microcontrollers or FPGAs without level-shifting circuitry-confirmed in the "Inputs Tolerant Down to 2 V" feature and Electrical Characteristics tables for SNx4S24x.

What is the purpose of the hysteresis on SN74S240DWR inputs?

The hysteresis (0.2–0.4 V) on SN74S240DWR inputs increases noise immunity by creating separate voltage thresholds for rising and falling edges. This prevents false triggering from slow-rising or noisy signals-especially valuable in electrically harsh environments like server backplanes or industrial control cabinets. It is explicitly documented in Section 6.6 (Electrical Characteristics – SNx4S24x) and Feature Description (Section 8.3.3).

Can the SN74S240DWR drive a 133-Ω terminated line?

Yes, the SN74S240DWR is explicitly rated to drive terminated lines down to 133 Ω, as stated in the device description (page 1) and confirmed by its 64 mA low-level output current (IOL) specification. This capability enables clean signal transmission over controlled-impedance PCB traces or cables without external termination resistors, a key advantage over LS-family equivalents.

How should the output-enable (G) pins be handled during power-up?

To ensure outputs remain in high-impedance state during power-up or power-down, both 1G and 2G pins must be tied to VCC through pullup resistors. The minimum resistor value depends on the current-sinking capability of the controlling driver, as detailed in Section 8.1 (Overview). Leaving G pins floating risks undefined output states and potential bus contention.