Texas Instruments SN74HCT240NS

Overview

SN74HCT240NS from Texas Instruments is an octal inverting buffer/line driver with 3-state outputs, designed for memory address and bus driving in industrial control and embedded systems. It operates at 4.5–5.5 V, delivers ±6 mA output drive, exhibits 12 ns typical propagation delay, and draws ≤80 μA supply current. Its dual 4-bit architecture with independent OE controls enables bidirectional bus isolation in microcontroller peripheral interfaces.

For engineers reviewing the SN74HCT240NS datasheet, SN74HCT240NS pinout, SN74HCT240NS application, or SN74HCT240NS equivalent, this page provides verified functional identity, SOP-20 package mapping, TTL-compatible input thresholds, 3-state timing parameters, and validated drop-in alternatives for bus interface redesigns and legacy system refreshes.

Technical Context

The SN74HCT240NS implements two independent 4-bit inverting buffers, each with dedicated output-enable (OE) inputs controlling high-impedance state entry/exit. Its HCT logic family ensures TTL-voltage compatibility (VIH = 2.0 V, VIL = 0.8 V) while maintaining CMOS power efficiency. All inputs are internally clamped to support robust noise immunity in noisy industrial environments.

Each buffer section drives up to 15 LSTTL loads with rail-to-rail output swing and supports CL = 50 pF and CL = 150 pF load conditions. The device features low input current (≤1 μA), fast enable/disable timing (ten/tdis ≤ 44 ns at 5.5 V), and guaranteed operation across –40°C to +85°C ambient temperature range.

Key Specifications

Pinout & Package

SOP-20 (NS) package: 12.6 mm × 7.8 mm body size, 1.27 mm pitch, gull-wing leads, RoHS-compliant NiPdAu finish, MSL Level-1 (260°C peak reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT240NS, SN74HCT240DWR offers identical functionality in a legacy SOIC-20 footprint for backward-compatible upgrades, while SN74ACT240NSR trades 5× higher quiescent current for 33% faster switching and 4× stronger output drive-ideal for high-noise, high-speed bus environments.

Availability

SN74HCT240NS is available at Aetrix Electronics and suitable for industrial control systems, embedded memory interfaces, and legacy equipment refurbishment requiring stable component supply and long-term lifecycle assurance.

Supply support for SN74HCT240NS 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 specializing in analog, embedded processing, and logic solutions with over 50 years of industrial-grade product development.

The SN74HCT240NS belongs to TI's 74HCT logic family, engineered for TTL-compatible operation in industrial automation, test equipment, and legacy system replacements where reliability and pin-for-pin compatibility are critical.

FAQ

What is the operating voltage range for SN74HCT240NS?

The SN74HCT240NS operates from 4.5 V to 5.5 V. This range ensures compatibility with standard 5 V power rails and accommodates typical ±5% regulation tolerance. Operation outside this range may cause undefined behavior or permanent damage, as specified in the absolute maximum ratings table of the TI datasheet SCLS174H.

Does SN74HCT240NS support true 3-state outputs?

Yes, SN74HCT240NS provides true high-impedance 3-state outputs controlled by active-low OE pins (1OE and 2OE). When either OE is high, its associated four outputs enter high-Z mode with leakage ≤±5 μA at 5.5 V, enabling safe bus sharing without contention or signal corruption.

Is SN74HCT240NS pin-compatible with older 74LS240 devices?

Yes, SN74HCT240NS uses the same SOP-20 pinout as 74LS240 and other members of the 74x240 family. All input/output assignments-including dual OE controls, inverted A→Y mapping, and VCC/GND positions-are identical, enabling direct replacement in legacy designs without PCB modification.

What is the maximum capacitive load SN74HCT240NS can drive reliably?

SN74HCT240NS is characterized for CL = 50 pF and CL = 150 pF loads. At 5.5 V, it maintains tpd ≤ 33 ns and ten ≤ 40 ns into 150 pF, supporting robust operation with typical PCB trace capacitance plus multiple gate inputs-no external termination needed for standard bus lengths.

How does SN74HCT240NS handle unused inputs?

All unused inputs on SN74HCT240NS must be tied to VCC or GND to prevent floating states that cause excessive current draw or oscillation. TI recommends connecting unused A inputs to GND (for logic-low default) or VCC (for logic-high default), consistent with the device's function table and layout guidelines in SCLS174H Section 7.2.