Texas Instruments SN74HC240N

Overview

SN74HC240N 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 from 2V to 6V, delivers ±6mA output drive at 5V, exhibits typical propagation delay of 9ns, and consumes ≤80µA ICC - enabling low-power, high-density bus interfacing in 8-bit data paths.

For engineers reviewing the SN74HC240N datasheet, SN74HC240N pinout, SN74HC240N application, or SN74HC240N equivalent, this page provides verified functional modes, thermal metrics for PDIP-20 packaging, real-world switching characteristics under 50pF/150pF loads, and validated alternatives for bus isolation and address buffering in legacy-compatible designs.

Technical Context

The SN74HC240N implements two independent 4-bit inverting buffers, each controlled by a dedicated output-enable (OE) input. When OE is low, inverted logic passes from A inputs to Y outputs; when OE is high, all eight outputs enter high-impedance state - enabling bidirectional bus contention management without external logic.

Its CMOS HCMOS architecture ensures rail-to-rail output swing, low input current (≤1µA), and compatibility with LSTTL loads (up to 15). The device supports wide VCC range (2–6V), operates from –40°C to +85°C, and features defined VIH/VIL thresholds across supply voltages per JEDEC JESD8-5.

Key Specifications

Pinout & Package

SN74HC240N uses a 20-pin plastic dual in-line package (PDIP) with 0.300" body width and 0.100" lead pitch. Pin 1 is located at the left end of the top row, identified by a notch or dot. Thermal resistance RθJA is 84.6°C/W, supporting operation up to +85°C ambient without forced airflow.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC240N, SN74HCT240N offers guaranteed TTL input compatibility at no PCB change, while 74AC240N delivers superior speed and drive at increased power cost - making SN74HC240N optimal for cost-sensitive, low-power industrial interfaces where 9ns delay suffices.

Availability

SN74HC240N is available at Aetrix Electronics and suitable for industrial control panels, legacy test equipment upgrades, and embedded memory subsystems requiring stable component supply with long-term lifecycle support.

Supply support for SN74HC240N 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 ICs, with decades of experience in industrial-grade logic families.

The SN74HC240N belongs to TI's 74HC high-speed CMOS logic series, engineered for low-power, noise-immune bus interfacing in harsh industrial and automotive environments.

FAQ

What is the function of the OE pins on the SN74HC240N?

The SN74HC240N has two active-low output-enable pins: 1OE (pin 1) controls the first four inverters (1A1→1Y1 through 1A4→1Y4), and 2OE (pin 19) controls the second four (2A1→2Y1 through 2A4→2Y4). When an OE pin is low, its associated group passes inverted input data to outputs; when high, those outputs go high-impedance - enabling selective bus access without external gating logic.

Can SN74HC240N operate at 3.3V supply voltage?

Yes, SN74HC240N is fully specified from 2V to 6V, including 3.3V operation. At VCC = 3.3V, it maintains VIH ≥2.31V and VIL ≤0.99V, ensuring reliable interfacing with 3.3V microcontrollers. Output drive is ±4mA typical, sufficient for most 3.3V CMOS loads and light-duty bus termination.

Is SN74HC240N pin-compatible with SN74LS240?

No, SN74HC240N is not pin-compatible with SN74LS240. While both are octal inverting 3-state buffers, SN74LS240 uses a different pin assignment: its OE inputs are on pins 1 and 19 but drive non-inverting outputs, and its input/output pairing differs. Physical insertion into an LS240 footprint will cause functional failure and potential damage due to incorrect signal routing.

What thermal considerations apply to SN74HC240N in PDIP package?

SN74HC240N in PDIP-20 has RθJA = 84.6°C/W. At 85°C ambient and 80µA ICC, self-heating is negligible (<7°C rise); however, under worst-case switching (all outputs toggling at 10MHz into 50pF), junction temperature must be calculated using Cpd = 35pF/buffer. Derating is required above 70°C ambient if sustained high-frequency operation is expected.

How should unused inputs be handled on SN74HC240N?

All unused inputs on SN74HC240N must be tied to a valid logic level - either VCC or GND - to prevent floating nodes that cause excessive ICC, oscillation, or ESD susceptibility. Do not leave inputs open. For unused OE pins, tie to VCC to disable the corresponding buffer group; for unused A inputs, tie to GND (to force Y = high-Z when OE is active) or VCC (to force Y = low when OE is active), depending on system default state requirements.