Texas Instruments SN74ALS540N3

Overview

SN74ALS540N from Texas Instruments is an octal inverting buffer/line driver with 3-state outputs, designed for bus interfacing and memory address register buffering in TTL-compatible digital systems. It operates at 4.5–5.5 V, delivers up to 24 mA low-level output current (48 mA for -1 variant), features dual 3-state enable inputs (OE1/OE2), and uses a data flowthrough pinout with inputs and outputs on opposite sides of the 20-pin PDIP package.

For engineers reviewing the SN74ALS540N datasheet, SN74ALS540N pinout, SN74ALS540N application, or SN74ALS540N equivalent, this device is selected for high-drive, low-propagation-delay bus buffering where inverted logic and 3-state control are required in legacy industrial, test equipment, and embedded controller designs.

Technical Context

The SN74ALS540N implements eight independent inverting buffer channels, each with a 2-input NOR gate-based 3-state control enabling simultaneous high-impedance output disable via either OE1 or OE2. Its pnp input structure reduces DC loading on driving sources, improving fan-out capability in dense TTL bus environments.

Propagation delays are specified at 2–12 ns (tPHL/tPLH) and 3-state enable/disable times range from 1–28 ns (tPHZ/tPZL), optimized for synchronous bus arbitration and memory address latching. All timing parameters are guaranteed over 0°C to 70°C with CL = 50 pF and R1/R2 = 500 Ω.

Key Specifications

Pinout & Package

SN74ALS540N is housed in a 20-pin plastic dual in-line package (PDIP-N), 7.62 mm pitch, 24.13 mm body length, with JEDEC MS-001 compliant footprint and through-hole mounting compatibility.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ALS540N-1 and SN74LS240N, the SN74ALS540N delivers optimal balance of speed (≤12 ns), drive strength (24 mA), and input loading (IIL ≤ –0.2 mA) for general-purpose 5 V TTL bus buffering without over-specifying current capability or sacrificing timing.

Availability

SN74ALS540N is available at Aetrix Electronics and suitable for memory address buffering, parallel bus isolation, test equipment signal conditioning, and industrial I/O expansion requiring stable component supply and long-term industrial lifecycle support.

Supply support for SN74ALS540N 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 founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial, automotive, and communications portfolio coverage.

The SN74ALS540N belongs to the 74ALS advanced low-power Schottky logic family, engineered for high-speed, low-power TTL-compatible interfacing in mission-critical industrial and instrumentation systems.

FAQ

What is the logic function of the SN74ALS540N?

The SN74ALS540N is an octal inverting buffer with 3-state outputs. Each of its eight channels accepts a TTL-level input (A1–A8), inverts it, and presents the result at the corresponding output (Y1–Y8). When either OE1 or OE2 is high, all outputs enter high-impedance state. This makes SN74ALS540N ideal for bidirectional bus control and memory address latching where signal inversion and isolation are both required.

Does the SN74ALS540N support 3.3 V operation?

No, the SN74ALS540N is not rated for 3.3 V operation. Its recommended operating supply voltage is strictly 4.5 V to 5.5 V, with absolute maximum VCC at 7 V. Input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and output drive characteristics are specified only within the 5 V TTL domain. Using SN74ALS540N with 3.3 V supplies risks undefined behavior, insufficient noise margin, and potential damage if VI exceeds VCC + 0.5 V.

What is the difference between SN74ALS540N and SN74ALS540N-1?

The SN74ALS540N-1 is a higher-drive variant of the SN74ALS540N, rated for 48 mA low-level output current (IOL) under tight VCC conditions (4.75–5.25 V), versus 24 mA for the standard SN74ALS540N. All other electrical and timing specifications-including propagation delay, input thresholds, and pinout-are identical. The -1 suffix denotes enhanced output drive capability, not a different package or logic function.

Can SN74ALS540N replace SN74LS240N in existing designs?

Yes, SN74ALS540N is pin-compatible and functionally equivalent to SN74LS240N, with identical pinout, logic function, and 3-state control. However, SN74ALS540N offers faster propagation delay (≤12 ns vs. ≤25 ns), lower input current (IIL ≤ –0.2 mA vs. ≈ –0.4 mA), and improved noise immunity. No PCB changes are required, but verify timing margins and load conditions-especially if operating near maximum frequency-due to the speed improvement.

What package type does SN74ALS540N use, and is it RoHS-compliant?

SN74ALS540N uses a 20-pin plastic dual in-line package (PDIP-N) with lead finish NIPDAU (nickel/palladium/gold), and is RoHS-compliant (per TI's packaging addendum). The package has 2.54 mm pitch, 7.62 mm row spacing, and 24.13 mm body length. It is intended for through-hole assembly and supports wave or selective soldering processes per JEDEC MS-001 standards.