onsemi MC74ACT540MELG

Overview

MC74ACT540MELG from onsemi is an octal inverting buffer/line driver with 3-state outputs, designed for memory and address bus interfacing, clock distribution, and bidirectional data transmission. It operates at 4.5 V to 5.5 V, delivers ±24 mA output drive, supports −40°C to +85°C ambient operation, and features TTL-compatible inputs - used in microprocessor I/O port expansion and industrial control backplanes.

For engineers reviewing the MC74ACT540MELG datasheet, pinout, applications, or equivalent options, key selection criteria include 3-state enable timing (tPZH/tPLZ ≤ 11.5 ns), flow-through pinout for PCB layout efficiency, inverted logic function, and SOIC-20W Pb-free packaging compliance.

Technical Context

The MC74ACT540MELG implements eight independent inverting buffers, each with dual active-low 3-state enable inputs (OE1 and OE2) controlling all outputs simultaneously. Its flow-through architecture places inputs on pins 1–10 and outputs on pins 11–20, enabling direct microprocessor bus connection without signal layer crossover.

It uses advanced CMOS technology with TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max at VCC = 5.5 V), guarantees rail-to-rail output swing (VOH ≥ 4.4 V, VOL ≤ 0.44 V at IOL/IOH = ±24 mA), and maintains low dynamic power dissipation (CPD = 30 pF).

Key Specifications

Pinout & Package

MC74ACT540MELG is housed in a 20-pin SOIC-Wide (Case 751D) package with 1.27 mm pitch, 7.5 mm body width, and 12.8 mm length. Pin 1 is marked by a beveled corner or notch; pin 10 is GND, pin 20 is VCC.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MC74ACT540DWG, MC74ACT540MELG offers identical performance in a tape-and-reel format optimized for production; versus SN74ACT540N, it provides superior output voltage margins and lower capacitive loading - critical for timing-critical or high-noise industrial bus applications.

Availability

MC74ACT540MELG is available at Aetrix Electronics and suitable for microprocessor I/O expansion, memory address buffering, and industrial control backplane applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant sourcing.

Supply support for MC74ACT540MELG 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

onsemi is a global semiconductor manufacturer specializing in energy-efficient, high-performance analog, logic, and discrete components for automotive, industrial, and cloud infrastructure markets.

The MC74ACT540MELG belongs to onsemi's 74ACT logic family, engineered for high-speed, low-power 5 V TTL-compatible digital interfacing in mission-critical industrial and computing systems.

FAQ

What is the logic function of the MC74ACT540MELG?

The MC74ACT540MELG is an octal inverting buffer with 3-state outputs. Each of its eight channels accepts a digital input (D1–D8), inverts it, and drives the corresponding output (Q1–Q8) when both OE1 and OE2 are asserted low. When either enable is high, all outputs enter high-impedance state - making MC74ACT540MELG ideal for bidirectional bus applications where multiple devices share a common data path.

Does MC74ACT540MELG support 3.3 V operation?

No, MC74ACT540MELG is specified only for 4.5 V to 5.5 V supply operation per its Recommended Operating Conditions. It is not rated for 3.3 V use. For 3.3 V systems, consider the 74LVC540 or 74ALVC540 families instead. Attempting to operate MC74ACT540MELG below 4.5 V may result in undefined logic levels, increased propagation delay, or failure to meet VOH/VOL specifications.

What is the meaning of "MELG" in MC74ACT540MELG?

The suffix "MELG" identifies the specific packaging and environmental compliance of this variant: "ME" denotes tape-and-reel packaging in SOIC-20W (Case 751D), "L" indicates lead-free (Pb-free) construction, and "G" confirms RoHS compliance. This matches onsemi's standard marking convention and distinguishes it from rail-packaged variants like MC74ACT540DWG.

How does the dual-enable (OE1/OE2) architecture improve system reliability?

The MC74ACT540MELG requires both OE1 and OE2 to be low to enable outputs - a design that prevents accidental bus activation during power sequencing or reset events. If only one enable is asserted, outputs remain in high-impedance state. This redundancy reduces risk of bus contention in complex systems where multiple control signals manage data flow, enhancing robustness in industrial PLCs and embedded controllers using MC74ACT540MELG.

Is MC74ACT540MELG pin-compatible with older 74AC540 devices?

Yes, MC74ACT540MELG shares identical pinout, package dimensions, and logic function with MC74AC540 and 74AC540 variants. However, MC74ACT540MELG features TTL-compatible inputs (VIH = 2.0 V min), whereas 74AC540 requires higher VIH (2.1 V min at VCC = 5.5 V). This makes MC74ACT540MELG a functional upgrade for systems interfacing with standard TTL outputs, while retaining full mechanical and electrical compatibility with existing 74AC540 footprints.