Texas Instruments SN74AS240N

Overview

SN74AS240N from Texas Instruments is an octal inverting buffer/driver with 3-state outputs, designed for memory address driving, bus interfacing, and clock distribution in TTL-based systems. It operates at 5 V (4.5–5.5 V), delivers 64 mA low-level output current, features pnp inputs to reduce DC loading, and supports 0°C to 70°C industrial temperature range.

For engineers reviewing the SN74AS240N datasheet, SN74AS240N pinout, SN74AS240N application, or SN74AS240N equivalent, key selection criteria include its 3-state bus-driving capability, high-speed propagation (≤6.5 ns), TTL-compatible input/output levels, and standard 20-pin plastic DIP (N) package.

Technical Context

This device implements two independent 4-bit inverting buffer groups, each controlled by a dedicated active-low output-enable (OE̅) input. Its architecture enables symmetrical bus arbitration-both OE̅ pins must be asserted low to activate outputs, and either can disable all eight outputs independently.

It uses Advanced Schottky (AS) bipolar technology, delivering faster switching than ALS variants (e.g., tPHL ≤6.5 ns vs. ≤9 ns), lower propagation delay skew, and higher drive strength (IOL = 64 mA vs. 24 mA for SN74ALS240A), while maintaining TTL input thresholds (VIL = 0.8 V, VIH = 2 V) and output voltage compliance (VOH ≥2.4 V, VOL ≤0.55 V at IOL = 64 mA).

Key Specifications

Pinout & Package

SN74AS240N is supplied in a 20-pin plastic dual in-line package (PDIP), 300-mil width, with standard through-hole mounting and JEDEC MO-015AC footprint.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal inverting 3-state buffer applications.

Compared with SN74ALS240N and SN74F240N, SN74AS240N provides superior bus-driving strength and speed for demanding memory and clock applications, while retaining full pin compatibility and TTL interface behavior-making it the optimal upgrade path where performance headroom is critical.

Availability

SN74AS240N is available at Aetrix Electronics and suitable for memory address buffering, system bus interfacing, clock distribution, and legacy bus isolation requiring stable component supply and long-term industrial availability.

Supply support for SN74AS240N 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 solutions for industrial, automotive, and communications markets.

SN74AS240N belongs to TI's Advanced Schottky (AS) logic family, engineered for high-speed, high-drive digital interfacing in memory, bus, and clock subsystems where performance exceeds ALS and F-series capabilities.

FAQ

What is the maximum recommended output current for SN74AS240N?

The SN74AS240N is rated for a maximum low-level output current (IOL) of 64 mA per output under recommended operating conditions (VCC = 4.5–5.5 V, TA = 0°C to 70°C). This value is confirmed in the electrical characteristics table for SN74AS240A, and applies directly to SN74AS240N as the N-suffix denotes the standard plastic DIP package variant of SN74AS240A. Exceeding this current risks VOL degradation or thermal stress.

Does SN74AS240N support mixed-voltage operation, such as 3.3 V inputs?

No, SN74AS240N is a TTL-family device with fixed input thresholds (VIL = 0.8 V, VIH = 2.0 V) and 5 V supply dependency. It does not support 3.3 V logic-level inputs without external level translation. The absolute maximum input voltage is 7 V, but functional operation requires VI within the recommended 0–VCC range and adherence to TTL-compatible voltage levels. SN74AS240N must be used in 5 V systems with other TTL or compatible sources.

Can SN74AS240N replace SN74ALS240N in an existing design?

Yes, SN74AS240N is pin-compatible and functionally identical to SN74ALS240N, with identical pinout, logic behavior, and 3-state control. However, SN74AS240N offers higher drive (64 mA vs. 24 mA) and faster speed (6.5 ns vs. 9 ns propagation), so it may improve timing margins and bus loading capacity. No PCB changes are required, but verify that increased ICC (up to 75 mA active) and faster edge rates do not introduce noise or crosstalk in the target layout.

What is the purpose of the two separate OE̅ inputs on SN74AS240N?

The two active-low output-enable inputs (1OE̅ and 2OE̅) provide independent control over two isolated 4-bit inverting buffer groups. This allows SN74AS240N to manage dual bus segments-for example, enabling upper/lower memory banks separately or isolating data/control paths without additional logic. Each OE̅ disables only its associated four outputs, preserving signal integrity and reducing contention risk during partial bus access.

Is SN74AS240N suitable for use in automotive applications?

SN74AS240N is characterized for 0°C to 70°C operation and is not qualified for automotive AEC-Q100 temperature grades (–40°C to 125°C). While it may function in benign under-hood environments, TI does not guarantee reliability or parametric performance outside its specified commercial temperature range. For automotive applications, consider automotive-qualified alternatives such as SN74AHCT240QPWRQ1 or consult TI's automotive logic portfolio-SN74AS240N itself is not intended for safety-critical or extended-temperature vehicle systems.