onsemi MC74AC240DW

Overview

MC74AC240DW from onsemi is an octal 3-state buffer/line driver in SOIC-20W package, operating at 2.0–6.0 V supply, delivering ±24 mA output drive, with propagation delay as low as 4.5 ns (VCC = 5.0 V), and designed for memory address driving, clock distribution, and bidirectional bus interfacing in industrial control and embedded systems.

For engineers reviewing the MC74AC240DW datasheet, pinout, applications, or equivalent options, this page delivers verified electrical parameters, truth-table–validated 3-state control logic, SOIC-20W mechanical dimensions, thermal resistance (96 °C/W), and direct alternatives with documented functional divergence.

Technical Context

The MC74AC240DW implements dual independent 4-bit non-inverting buffers, each controlled by a dedicated 3-state enable (OE1/OE2), supporting simultaneous or staggered bus isolation. Its CMOS AC logic family ensures TTL-compatible voltage thresholds only in ACT variants - this AC variant uses standard CMOS input thresholds (VIH = 2.1 V @ VCC = 3.0 V).

It features rail-to-rail output swing (VOH ≥ 2.9 V @ VCC = 3.0 V, VOL ≤ 0.1 V), high-impedance off-state leakage < ±5.0 µA, and operates across −40 °C to +85 °C ambient. No internal clamping diodes are specified beyond absolute maximum ratings; external protection is required per application.

Key Specifications

Pinout & Package

MC74AC240DW is housed in a Pb-free SOIC-20 Wide Body (Case 751D) package, 12.95 mm × 7.60 mm × 2.65 mm, with 1.27 mm pitch, gull-wing leads, and JEDEC-standard pin numbering.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74AC240N and MC74ACT240DW, the MC74AC240DW offers optimal thermal performance in surface-mount industrial layouts and native compatibility with 3.3 V CMOS logic levels - making it preferred for compact, thermally constrained embedded controllers.

Availability

MC74AC240DW is available at Aetrix Electronics and suitable for industrial PLC I/O modules, microcontroller bus expansion, and memory address buffering requiring stable component supply, long-term lifecycle support, and RoHS-compliant sourcing.

Supply support for MC74AC240DW 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 (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient silicon solutions for automotive, industrial, cloud, medical, and IoT applications.

The MC74AC240DW belongs to onsemi's legacy AC logic family, engineered for high-speed, low-power bus interfacing in industrial control and embedded computing systems where reliability and wide supply tolerance are critical.

FAQ

What is the maximum operating frequency supported by the MC74AC240DW?

The MC74AC240DW does not specify a maximum clock frequency in its datasheet because it is a combinational buffer, not a clocked device. However, its propagation delay (tPLH/tPHL ≤ 7.0 ns at VCC = 5.0 V, CL = 50 pF) supports reliable operation in bus systems with signal periods exceeding 14 ns - corresponding to effective data rates up to ~70 MHz for single-edge-triggered interfaces. System-level timing must account for board trace delays and load capacitance.

Does the MC74AC240DW support mixed-voltage operation between 3.3 V and 5 V domains?

Yes, the MC74AC240DW supports mixed-voltage operation: its VCC range is 2.0–6.0 V, and its input thresholds scale with VCC (e.g., VIH = 2.1 V @ 3.0 V, 3.15 V @ 4.5 V). When powered at 3.3 V, it reliably accepts 3.3 V logic inputs and drives 3.3 V loads; when powered at 5.0 V, it interfaces with 5 V TTL/CMOS. Level shifting is not required within these rails.

How are the two 3-state enable inputs (OE1 and OE2) used in practice?

The MC74AC240DW provides two independent active-low 3-state enables: OE1 controls outputs Y1–Y4 (pins 2,4,6,8), and OE2 controls Y5–Y8 (pins 11,13,15,17). This allows partitioning of the 8-bit bus - for example, using OE1 for address bits A0–A3 and OE2 for A4–A7 during segmented memory access, or enabling/disabling halves of a data bus independently to prevent contention in multi-master systems.

Is the MC74AC240DW pin-compatible with the MC74ACT240DW?

Yes, the MC74AC240DW and MC74ACT240DW share identical pinout, package (SOIC-20W), and DC/AC specifications except for input voltage thresholds: the ACT version has TTL-compatible inputs (VIH = 2.0 V fixed), while the AC version has CMOS-ratio inputs (VIH ≈ 0.7×VCC). They are drop-in replacements only when input logic family matches - substituting one for the other without verifying source logic levels may cause recognition failures.

What is the thermal performance of the MC74AC240DW in continuous operation?

The MC74AC240DW in SOIC-20W package has a junction-to-ambient thermal resistance (θJA) of 96 °C/W. At maximum rated ambient temperature (85 °C) and VCC = 5.5 V, total power dissipation must remain below ~350 mW to keep junction temperature ≤140 °C. Under typical 24 mA output loading across four channels, dynamic power remains well within this limit - measured ICC < 80 µA quiescent confirms minimal self-heating in idle states.