onsemi MC74AC646DWG

Overview

MC74AC646DWG from onsemi is an octal registered transceiver with 3-state outputs, non-inverting data path, dual independent A/B bus registers, and real-time or stored-data multiplexed transfer capability. It operates at 2.0–6.0 V supply, delivers ±24 mA output drive, and supports bidirectional data flow between 8-bit buses in industrial control and memory interface applications.

For engineers reviewing the MC74AC646DWG datasheet, pinout, applications, or equivalent options, key selection criteria include clock-controlled register loading (CAB/CBA), dual-direction transmit/receive control (SAB/SBA), output enable logic (DIR/G), 24-pin SOIC-WB package compatibility, and AC-series voltage tolerance up to 6.0 V.

Technical Context

The MC74AC646DWG implements two independent 8-bit D-type flip-flop registers-one per bus-enabling simultaneous storage of A- and B-bus data on LOW-to-HIGH clock transitions. Its control logic decodes combinations of DIR, G, SAB, SBA, CAB, and CBA to select among four fundamental operations: real-time A→B, real-time B→A, stored-A→B, and stored-B→A transfers.

Output enable is managed by active-low G and direction-select DIR inputs, where G disables all outputs into high-impedance state regardless of DIR, while DIR determines bus directionality when G is asserted. Propagation delays range from 1.0 ns (bus-to-bus) to 13.5 ns (clock-to-bus) at 5.0 V, with setup/hold times as low as 1.0 ns and 0.5 ns respectively under recommended conditions.

Key Specifications

Pinout & Package

MC74AC646DWG is housed in a 24-pin SOIC-Wide Body (SOIC-24 WB) package per case outline 751E, with 0.60 mm lead thickness, 15.4 mm × 7.5 mm body dimensions, and 1.27 mm pitch. Pin 1 is marked with a notch or dot; leads are gull-wing shaped and Pb-free.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal registered transceiver applications.

Compared with MC74ACT646DWG, the MC74AC646DWG supports broader supply range (2.0–6.0 V vs. 4.5–5.5 V) but lacks TTL input compatibility; versus SN74ABT646DBR, it offers lower power and industry-standard SOIC-24 fit but trades off drive strength and speed for robustness in general-purpose industrial interfaces.

Availability

MC74AC646DWG is available at Aetrix Electronics and suitable for industrial PLC backplane interfaces, legacy memory bus extensions, test equipment signal routing, automated test fixture control, and embedded controller I/O expansion requiring stable component supply and long-term manufacturability.

Supply support for MC74AC646DWG 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 delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The MC74AC646DWG belongs to the 74AC logic family designed for high-speed, low-power, wide-supply-range digital interfacing in industrial and embedded systems where reliability and interoperability across voltage domains are essential.

FAQ

What is the maximum operating supply voltage for MC74AC646DWG?

The MC74AC646DWG supports a DC supply voltage range of −0.5 V to +7.0 V, with recommended operation from 2.0 V to 6.0 V. Absolute maximum rating of +7.0 V applies only for short-duration transients; continuous operation above 6.0 V risks parametric shift or reliability degradation. The MC74AC646DWG must be operated within 2.0–6.0 V for guaranteed timing, drive strength, and logic threshold compliance per its datasheet specifications.

Does MC74AC646DWG support true bidirectional data flow between A and B buses?

Yes, the MC74AC646DWG supports full bidirectional operation via separate SAB (A-to-B enable) and SBA (B-to-A enable) control inputs, combined with DIR and G. When SAB is active, data flows from A bus to B bus either in real-time or from A register; when SBA is active, data flows from B bus to A bus similarly. The MC74AC646DWG does not auto-detect direction - explicit control signal sequencing is required for safe bus arbitration.

What is the function of the CAB and CBA pins on MC74AC646DWG?

CAB and CBA are dedicated clock inputs that trigger LOW-to-HIGH transitions to load data from the respective A or B bus into their corresponding internal D-type registers. CAB clocks A-bus data into the A register; CBA clocks B-bus data into the B register. These clocks operate independently, allowing asynchronous capture of data on each bus. The MC74AC646DWG requires clean, monotonic clock edges meeting specified rise/fall time limits to avoid metastability or partial register updates.

Can MC74AC646DWG be used in 3.3 V systems?

Yes, the MC74AC646DWG is fully specified for operation at 3.3 V (VCC = 3.3 V ±0.3 V), with guaranteed VIH = 2.1 V, VIL = 0.9 V, VOH ≥ 2.9 V, VOL ≤ 0.1 V, and tPLH/tPHL ≤ 18.5 ns. Its AC and DC characteristics are validated across −40 °C to +85 °C at 3.3 V, making the MC74AC646DWG suitable for mixed-voltage 3.3 V/5 V system interfaces without level-shifting circuitry.

Is MC74AC646DWG pin-compatible with MC74ACT646DWG?

Yes, the MC74AC646DWG and MC74ACT646DWG share identical pinout, package (SOIC-24 WB), functional block diagram, and register architecture. The sole difference is input threshold compatibility: MC74ACT646DWG has TTL-compatible inputs (VIH = 2.0 V, VIL = 0.8 V), while MC74AC646DWG uses CMOS thresholds (VIH = 2.1 V, VIL = 0.9 V at 3.0 V). Both devices are mechanically and electrically interchangeable in the same footprint, though logic-level margin should be verified for each application.