Texas Instruments SN74LS240DWR

Overview

SN74LS240DWR 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 (1A–1Y and 2A–2Y), 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 SN74LS240DWR datasheet, SN74LS240DWR pinout, SN74LS240DWR application, or SN74LS240DWR equivalent, this page delivers verified functional modes, real-world bus-driving performance metrics, thermal resistance data (R_θJA = 94.3°C/W), and validated alternatives for memory address buffering, LED display multiplexing, and telecom line interface design.

Technical Context

The SN74LS240DWR implements two independent 4-bit inverting buffers, each controlled by a dedicated active-low output-enable (G) input (Pin 1 for Channel 1, Pin 19 for Channel 2). Its TTL-compatible inputs include built-in hysteresis (0.2–0.4 V) for noise immunity and tolerate down to 2 V, enabling interoperability with 3.3-V systems. Outputs switch between low-impedance logic states and high-impedance tri-state mode-critical for shared bus arbitration.

It uses standard LS (Low-Power Schottky) technology, delivering 24 mA sink current per output (I_OL) and –3 mA source current (I_OH) under recommended conditions. The device drives terminated lines down to 133 Ω and exhibits symmetrical enable/disable timing (t_PZH/t_PZL ≤ 23 ns), supporting reliable signal integrity in dense PCB layouts.

Key Specifications

Pinout & Package

SN74LS240DWR is housed in a 20-pin SSOP (Shrink Small Outline Package) with body size 7.20 mm × 5.30 mm and 0.65 mm lead pitch. This surface-mount package supports automated assembly and offers improved thermal performance over PDIP while maintaining pin compatibility with legacy SOIC footprints.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS244DWR, the SN74LS240DWR provides inverted outputs essential for address decoding pipelines, while SN74HC240PW trades LS noise robustness for CMOS power efficiency-making it viable only where hysteresis is not required and supply flexibility is critical.

Availability

SN74LS240DWR is available at Aetrix Electronics and suitable for memory address buffering, LED display multiplexing, telecom line interface, and network switch backplane driver applications requiring stable component supply across extended production lifecycles.

Supply support for SN74LS240DWR 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 for industrial, automotive, and communications markets.

The SN74LS240DWR belongs to TI's legacy 74LS logic family, engineered specifically to enhance density and performance of three-state memory address drivers, clock drivers, and bus-oriented receivers-targeting reliability-critical infrastructure equipment.

FAQ

What is the function of Pin 19 on the SN74LS240DWR?

Pin 19 is the 2G (Channel 2 output-enable) input, an active-low control terminal that places all Channel 2 outputs (2Y1–2Y4) into high-impedance state when driven HIGH. When 2G is LOW, the device passes inverted signals from 2A1–2A4 to corresponding 2Y outputs. This independent enable allows asynchronous gating of two bus segments - a key feature confirmed in the SN74LS240DWR datasheet's Pin Functions table and Functional Block Diagrams.

Can SN74LS240DWR interface directly with 3.3-V microcontrollers?

Yes, SN74LS240DWR accepts 3.3-V logic inputs reliably: its VIH(min) is 2.0 V and VIL(max) is 0.8 V under recommended operating conditions, ensuring valid HIGH/LOW recognition from 3.3-V devices. This 3.3-V/5-V interoperability is explicitly stated in the Features section and validated in Electrical Characteristics tables - no level-shifting circuitry is needed for control signal interfacing.

What is the maximum output current rating for SN74LS240DWR?

The SN74LS240DWR is rated for 24 mA sink current (I_OL) per output at V_CC = 4.75 V and T_A = 25°C, with VOL ≤ 0.5 V. Source current (I_OH) is –3 mA with VOH ≥ 2.4 V. These values are specified in Section 6.3 (Recommended Operating Conditions) and Table 6.5 (Electrical Characteristics – SNx4LS24x) of the official datasheet and define safe steady-state drive capability for TTL loads.

Does SN74LS240DWR include input hysteresis, and why does it matter?

Yes, SN74LS240DWR incorporates 0.2–0.4 V of input hysteresis (VT+ − VT−), explicitly documented in Electrical Characteristics tables. This hysteresis increases noise immunity on shared buses - critical in applications like telecom infrastructure or server backplanes where ground bounce or EMI could cause false triggering. It is a distinguishing feature versus standard TTL buffers and directly improves system-level reliability.

How does the thermal performance of SN74LS240DWR compare across packages?

For SN74LS240DWR (SSOP-20 package), R_θJA is 94.3°C/W - higher than PDIP (50.6°C/W) but lower than SOP (76.6°C/W), as published in Section 6.4 (Thermal Information). This value assumes JEDEC-standard PCB mounting and defines junction temperature rise under load: at 100 mW dissipation, ΔT_J ≈ 9.4°C. Designers must use this metric - not generic "low-power" claims - to validate thermal margins in enclosed industrial enclosures.