Texas Instruments SN74LS240NS

Overview

SN74LS240NS 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, 15 ns maximum propagation delay at 5 V, ±24 mA output drive capability, and PNP input structure reducing DC loading on buses. It operates in industrial temperature range (0°C to 70°C) and supports mixed-voltage interfacing with 3.3-V/5-V logic compatibility.

For engineers reviewing the SN74LS240NS datasheet, SN74LS240NS pinout, SN74LS240NS application, or SN74LS240NS equivalent, key selection criteria include its inverting 3-state output behavior, channel-independent enable control (1G/2G), noise-immune hysteresis inputs, and suitability for terminated bus driving down to 133 Ω.

Technical Context

The SN74LS240NS implements two independent 4-bit inverting buffer sections, each with active-low output-enable (1G and 2G) controlling high-impedance state. Its PNP input stage lowers input current draw, while built-in hysteresis improves noise immunity on bus lines. The device uses standard TTL-compatible logic thresholds (VIH = 2 V, VIL ≤ 0.7 V) and delivers rail-to-rail switching into 667 Ω loads with 45 pF capacitance.

It supports bidirectional bus isolation via separate G controls per channel and is optimized for memory address register buffering and clock distribution where fan-out, timing predictability, and bus contention avoidance are critical. Output disable timing (tPZH/tPLZ) and enable timing (tPZL/tPHZ) are specified to ensure clean bus arbitration.

Key Specifications

Pinout & Package

SN74LS240NS is supplied in a 20-pin plastic SOP (Small Outline Package) with body size 7.80 mm × 12.60 mm (NS package code). Pin spacing is 1.27 mm, and it is surface-mount compatible.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS244NS and SN74LS240N, the SN74LS240NS offers identical electrical performance in a space-saving SOP package, making it optimal for modern compact designs requiring inverting logic - whereas SN74LS244NS serves polarity-sensitive paths and SN74LS240N supports legacy assembly methods.

Availability

SN74LS240NS is available at Aetrix Electronics and suitable for memory address buffering, LED display multiplexing, network switch backplane interface, and industrial I/O expander applications requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS240NS 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 headquartered in Dallas, Texas, specializing in analog, embedded processing, and logic ICs with over 50 years of leadership in industrial and automotive electronics.

The SN74LS240NS belongs to TI's legacy LS (Low-power Schottky) logic family, engineered for reliable bus interfacing in memory systems, instrumentation, and industrial control where predictable timing, noise immunity, and robust drive capability are essential.

FAQ

What is the logic function of the SN74LS240NS?

The SN74LS240NS is an octal inverting buffer with 3-state outputs, organized as two independent 4-bit sections. Each section inverts inputs (A1–A4) to outputs (Y1–Y4) when its respective active-low enable (1G or 2G) is asserted. When either enable is high, the corresponding Y outputs enter high-impedance state. This behavior is confirmed in the device functional table and logic diagram of the official TI datasheet SDLS144D.

Does the SN74LS240NS support 3.3-V logic inputs?

Yes, the SN74LS240NS inputs are tolerant down to 2 V and compatible with 3.3-V logic levels, as explicitly stated in the Features section of the TI datasheet SDLS144D. This allows direct interfacing with 3.3-V microcontrollers or FPGAs without external level-shifting circuitry, provided VCC remains at 5 V and input voltages stay within absolute maximum ratings.

What is the maximum output drive capability of the SN74LS240NS?

The SN74LS240NS delivers ±24 mA output current - specifically, IOL = 24 mA (low-level sink) and IOH = –24 mA (high-level source) - under recommended operating conditions (VCC = 4.75 V to 5.25 V, TA = 0°C to 70°C). This value is specified in Section 6.3 (Recommended Operating Conditions) and verified in Electrical Characteristics Table 6.5 of the TI SDLS144D datasheet.

How does the hysteresis feature benefit the SN74LS240NS in noisy environments?

The SN74LS240NS incorporates 0.2–0.4 V of input hysteresis (VT+ − VT−), which widens the voltage threshold window between logic HIGH and LOW states. This directly improves noise margins on shared bus lines by preventing false toggling due to EMI, ground bounce, or signal reflections - a key advantage confirmed in the Features and Detailed Description sections of the TI SDLS144D datasheet.

Can the SN74LS240NS drive terminated transmission lines?

Yes, the SN74LS240NS is explicitly rated to drive terminated lines down to 133 Ω, as documented in the Description section of the TI SDLS144D datasheet. This capability enables reliable signal transmission across impedance-controlled PCB traces or backplane interconnects without external termination resistors, supporting robust memory and bus interface designs.