Texas Instruments SN74S240N3

Overview

SN74S240N3 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, active-low output-enable (G) inputs, 7 ns typical propagation delay at 5 V, ±64 mA output drive capability, and operates across 0°C to 70°C.

For engineers reviewing the SN74S240N3 datasheet, SN74S240N3 pinout, SN74S240N3 application, or SN74S240N3 equivalent, this page delivers verified electrical specs, package-confirmed pin functions, real-world use cases in bus buffering and memory addressing, and validated alternative options for system-level design continuity.

Technical Context

The SN74S240N3 implements Schottky transistor logic (S-TTL) with PNP input stages that reduce DC loading on upstream drivers. Its dual-channel architecture provides independent 4-bit inverting buffers, each controlled by a dedicated active-low output-enable input (1G and 2G).

Each channel drives terminated lines down to 133 Ω with symmetrical switching-tPLH and tPHL both 7 ns typ at RL = 90 Ω, CL = 50 pF-and incorporates input hysteresis (0.2–0.4 V) to improve noise immunity in noisy bus environments.

Key Specifications

Pinout & Package

SN74S240N3 is supplied in a 20-pin plastic dual in-line package (PDIP-N), body size 24.33 mm × 6.35 mm, with through-hole mounting and industry-standard lead pitch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS240N and SN74F240N, SN74S240N3 delivers balanced performance: faster than LS for timing-critical buses yet more noise-immune than F-series, making it optimal for mixed-signal industrial backplanes requiring reliability and moderate speed.

Availability

SN74S240N3 is available at Aetrix Electronics and suitable for memory address buffering, system bus isolation, LED display multiplexing, and legacy telecom line driving requiring stable component supply across extended production lifecycles.

Supply support for SN74S240N3 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, delivering analog and embedded processing solutions for industrial, automotive, and communications markets.

SN74S240N3 belongs to TI's legacy S-TTL logic portfolio, engineered specifically for high-drive, noise-tolerant bus interfacing in memory subsystems and industrial control backplanes.

FAQ

What logic family does SN74S240N3 belong to, and how does it differ from LS-TTL variants?

SN74S240N3 is a Schottky TTL (S-TTL) device, distinguished by its use of Schottky diodes to prevent transistor saturation-yielding faster switching (7 ns typ) and higher output drive (±64 mA) versus LS-TTL's 14 ns and ±24 mA. Unlike LS-TTL, SN74S240N3 maintains full S-TTL compatibility while offering improved noise immunity via built-in input hysteresis.

Can SN74S240N3 interface directly with 3.3-V logic inputs?

Yes, SN74S240N3 inputs tolerate voltages down to 2 V and are explicitly rated for compatibility with 3.3-V logic levels. Its VIH minimum is 2 V and VIL maximum is 0.8 V, allowing safe interfacing with 3.3-V CMOS outputs without level-shifting circuitry-provided the 3.3-V source can sink the SN74S240N3's IIL of –400 µA per input.

What is the maximum capacitive load SN74S240N3 can drive while maintaining specified timing?

Per the datasheet, SN74S240N3's switching characteristics are characterized at CL = 50 pF with RL = 90 Ω. While it can drive higher capacitance, propagation delay increases linearly beyond this point-e.g., at 100 pF, tPLH/tPHL degrades to ~10 ns. For reliable operation, keep total load (trace + receiver input + probe) ≤50 pF unless timing margins are relaxed.

How should unused inputs and outputs be handled on SN74S240N3?

Unused inputs must be tied to VCC or GND-not left floating-to prevent oscillation and excess current draw. Unused outputs may be left unconnected in 3-state mode (G = HIGH), but if permanently enabled, they must be terminated to avoid floating nodes. The 1G and 2G pins should be pulled high via ≤10 kΩ resistors to ensure defined high-impedance state during power-up.

Does SN74S240N3 support hot-swap or live-insertion into a powered backplane?

No, SN74S240N3 is not hot-swap rated. Its absolute maximum ratings specify no exposure to VCC before GND stabilization, and applying signal inputs prior to VCC ramp-up risks latch-up or parametric shift. For backplane applications requiring live insertion, add series current-limiting resistors and coordinate power sequencing via system-level supervisors.