onsemi MC74ACT646DWR2G

Overview

MC74ACT646DWR2G from onsemi is an octal registered bus transceiver with 3-state outputs and non-inverting data paths, implementing dual-directional real-time or registered data transfer between A and B buses. It features independent A/B registers, TTL-compatible inputs, 24 mA output drive, and operates at 4.5–5.5 V supply. Used in bidirectional data buffering and register-controlled bus isolation in industrial control backplanes.

For engineers reviewing the MC74ACT646DWR2G datasheet, pinout, applications, or equivalent options, key selection criteria include clock-controlled register loading (CAB/CBA), dual transmit/receive control (SAB/SBA), output enable logic (DIR/G), and SOIC-24 package compatibility for high-density PCB layouts.

Technical Context

The MC74ACT646DWR2G integrates eight D-type flip-flops per bus side (A and B), enabling synchronous latching of data on LOW-to-HIGH clock transitions at CAB or CBA. Its control architecture supports four distinct data-handling modes: real-time A→B, real-time B→A, stored-A→B, and stored-B→A - selected via SAB/SBA and DIR signals.

Output enable is managed by two independent active-low controls: G (global 3-state) and DIR (direction-selectable output enable). The device exhibits TTL-compatible input thresholds (VIH = 2.0 V, VIL = 0.8 V at VCC = 5 V) and guarantees 24 mA sink/source capability with VOL ≤ 0.44 V and VOH ≥ 4.4 V under load.

Key Specifications

Pinout & Package

MC74ACT646DWR2G is housed in a 24-pin SOIC wide-body (SOIC-24 WB) package per case outline 751E, with 1.27 mm pitch, 15.4 mm × 7.5 mm body size, and Pb-free finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT646DW and 74ACT646PC, the MC74ACT646DWR2G offers guaranteed MSL 1 handling, Pb-free compliance, and optimized SOIC-24 thermal resistance (59.8°C/W), making it the preferred choice for industrial-grade SMT production where long-term moisture resilience and regulatory conformance are mandatory.

Availability

MC74ACT646DWR2G is available at Aetrix Electronics and suitable for industrial backplane interfaces, microcontroller bus expansion, FPGA configuration bridges, and digital test equipment requiring stable component supply across extended temperature ranges and multi-year production cycles.

Supply support for MC74ACT646DWR2G 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 power management, analog, logic, and sensor solutions for automotive, industrial, and cloud infrastructure markets.

The MC74ACT646DWR2G belongs to the 74ACT logic family designed for high-speed, low-noise, TTL-compatible interfacing in industrial control and programmable logic systems where robust timing margins and bus integrity are critical.

FAQ

What is the maximum clock frequency supported by MC74ACT646DWR2G?

The MC74ACT646DWR2G does not specify a maximum clock frequency in its datasheet; instead, timing is defined by minimum pulse width (tw = 7.0 ns min at 5 V) and setup/hold requirements (ts = 7.0 ns, th = 2.5 ns). Based on propagation delays (max 16 ns clock-to-bus), reliable operation is achievable up to approximately 50 MHz in well-terminated, low-skew layouts. Always validate timing closure with actual board trace lengths and loading conditions for the MC74ACT646DWR2G.

Does MC74ACT646DWR2G support hot-swapping on a live bus?

The MC74ACT646DWR2G supports controlled hot-swap operation when G (global output enable) is held HIGH during insertion, placing all outputs in high-impedance state until system initialization completes. Its ±100 mA latchup immunity (per JESD78) and 2.0 V minimum VIH at 5 V supply ensure noise-immune enable sequencing. However, bus arbitration logic must be implemented externally - the MC74ACT646DWR2G itself provides no built-in hot-swap detection or current limiting.

Can MC74ACT646DWR2G operate at 3.3 V supply?

No, the MC74ACT646DWR2G is specified only for 4.5–5.5 V operation per its Recommended Operating Conditions table. While absolute maximum ratings allow VCC down to −0.5 V, functional operation below 4.5 V is not guaranteed: VIH/VIL thresholds are fixed for TTL compatibility, and output drive degrades significantly below 4.5 V. For 3.3 V systems, consider the MC74AC646DWR2G variant or level-shifting solutions - the MC74ACT646DWR2G must be used strictly within its 4.5–5.5 V range.

How are the DIR and G pins used together in MC74ACT646DWR2G?

In the MC74ACT646DWR2G, G is the global 3-state enable (active-low), while DIR selects data direction (A→B when DIR = LOW, B→A when DIR = HIGH). Both must be asserted correctly: G must be LOW to activate outputs, and DIR sets polarity. For example, to transmit A→B in real-time, set G = LOW, DIR = LOW, SAB = LOW, and apply clock to CAB. Misalignment (e.g., G = HIGH with DIR toggled) leaves outputs disabled regardless of DIR state - the MC74ACT646DWR2G requires coordinated control of both signals for valid operation.

Is MC74ACT646DWR2G pin-compatible with MC74AC646DWR2G?

Yes, the MC74ACT646DWR2G is pin-compatible and functionally identical to the MC74AC646DWR2G in SOIC-24 packaging, sharing identical pinout, register architecture, and control logic. The key difference lies in input threshold compatibility: MC74ACT646DWR2G has TTL-compatible inputs (VIH = 2.0 V), while MC74AC646DWR2G uses CMOS thresholds (VIH = 3.15 V at 4.5 V). Electrical substitution is possible only if driving sources meet the stricter VIH requirement of the MC74ACT646DWR2G.