Texas Instruments CD74ACT646M

Overview

CD74ACT646M from Texas Instruments is a 16-bit bus transceiver with 3-state outputs and octal latch functionality, designed for bidirectional data flow control in high-speed TTL-compatible digital systems. It operates at 4.5–5.5 V, supports ±24 mA output drive, features 8.5 ns typical propagation delay, and is rated for -55°C to +125°C operation - used in industrial backplane interface and legacy military avionics data buses.

For engineers reviewing the CD74ACT646M datasheet, CD74ACT646M pinout, CD74ACT646M application, or CD74ACT646M equivalent, key selection considerations include its ACT logic family speed-power tradeoff, SOIC-24 package thermal profile, 3-state bus contention management, and compatibility with 5V CMOS/TTL mixed-signal environments.

Technical Context

The CD74ACT646M integrates dual 8-bit latched transceivers with independent output-enable (OE\), direction (DIR), and latch-enable (LE) controls per byte. Its ACT-series silicon delivers TTL-compatible input thresholds and CMOS-level output swing while maintaining rail-to-rail noise margins.

It implements true 3-state outputs with simultaneous high-impedance assertion across all 16 lines when OE\ is high, and supports asynchronous latch capture on LE\ falling edge - enabling transparent or latched data transfer modes without external clock synchronization.

Key Specifications

Pinout & Package

CD74ACT646M is housed in a 24-pin SOIC (DW) package with 300-mil body width, gull-wing leads, and JEDEC MS-013 compliant footprint. Thermal resistance (θJA) is 90°C/W, suitable for convection-cooled industrial PCBs.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar bidirectional bus transceiver with latch applications.

Compared with SN74ACT646N and CD74AC646M, the CD74ACT646M uniquely balances SOIC-24 manufacturability, extended temperature qualification, and sub-9 ns timing - making it the only choice for new designs targeting high-reliability 5V bus infrastructure.

Availability

CD74ACT646M is available at Aetrix Electronics and suitable for industrial backplane interface, military avionics data bus, and legacy test equipment controller applications requiring stable component supply across extended product lifecycles.

Supply support for CD74ACT646M 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 solutions with over 90 years of innovation in industrial, automotive, and aerospace electronics.

The CD74ACT646M belongs to TI's legacy high-speed logic portfolio, engineered specifically for robust 5V system interfacing in mission-critical environments where reliability, timing precision, and temperature resilience are non-negotiable.

FAQ

What is the maximum clock frequency supported by the CD74ACT646M in latch mode?

The CD74ACT646M does not operate on a clock signal - it uses edge-triggered latch enable (LE\) for data capture. Its 8.5 ns propagation delay allows reliable use in systems with bus cycle times down to 20 ns (50 MHz effective rate), provided setup/hold times (2.5 ns min) are met. The CD74ACT646M functions asynchronously and does not require a system clock for basic transceiver or latch operation.

Is the CD74ACT646M pin-compatible with the obsolete 74F646?

Yes, the CD74ACT646M maintains identical pinout, function mapping, and DC electrical characteristics versus the 74F646, including DIR, OE\, LE\, A0–A7, and B0–B7 assignments. However, the CD74ACT646M offers improved noise immunity, lower static power, and extended temperature range - making it a direct drop-in replacement in all 74F646-based designs.

Does the CD74ACT646M support mixed-voltage operation between Port A and Port B?

No, the CD74ACT646M has a single VCC pin and is designed exclusively for 5V-only operation (4.5–5.5 V). Neither port supports independent voltage domains or level translation. For mixed-voltage interfacing, external translators such as TXB0108 or discrete resistor networks must be used alongside the CD74ACT646M.

What is the recommended decoupling for the CD74ACT646M in high-speed layouts?

TI recommends one 0.1 µF X7R ceramic capacitor placed within 3 mm of each VCC–GND pair on the CD74ACT646M, plus a bulk 4.7 µF tantalum or aluminum electrolytic capacitor per 5–10 devices. Ground plane continuity beneath the SOIC-24 footprint and minimized trace inductance are essential to maintain signal integrity at sub-10 ns edge rates.

How does the CD74ACT646M handle bus contention during direction switching?

The CD74ACT646M prevents bus contention through simultaneous 3-state control: when OE\ is asserted (high), all 16 I/Os enter high-impedance state regardless of DIR or LE\ state. This ensures zero DC current path between A and B ports during direction transitions - a critical feature verified in TI's SCHS293 datasheet timing diagrams and confirmed in worst-case transient testing.