Texas Instruments CD74HCT646M96

Overview

CD74HCT646M96 from Texas Instruments is an octal bus transceiver and register IC with 3-state outputs, designed for bidirectional data flow control between A and B 8-bit buses in industrial and embedded systems. It operates at 4.5–5.5 V, supports –55°C to 125°C temperature range, features independent A/B registers, and enables real-time or stored-data transfer via DIR, OE, CLKAB/CLKBA, and SAB/SBA controls - used in legacy bus arbitration and buffered memory interface circuits.

For engineers reviewing the CD74HCT646M96 datasheet, CD74HCT646M96 pinout, CD74HCT646M96 application, or CD74HCT646M96 equivalent, key selection criteria include TTL-compatible inputs, 3-state output drive capability (up to 15 LS-TTL loads), propagation delay ≤56 ns (CL = 50 pF), clock frequency up to 25 MHz, and SOIC-24 packaging for high-density PCB layouts.

Technical Context

The CD74HCT646M96 integrates eight identical channels, each containing a D-type flip-flop, 3-state output driver, and multiplexed input path. Its dual-clock architecture (CLKAB for A→register, CLKBA for B→register) enables asynchronous storage of data from either bus while maintaining transparent or registered transfer modes.

Direction control (DIR) selects bus flow direction during active output enable (OE low), while select controls (SAB/SBA) determine whether real-time or registered data appears on the output bus. Input functions remain enabled even when outputs are disabled, allowing concurrent data capture and isolation.

Key Specifications

Pinout & Package

CD74HCT646M96 is housed in a 24-pin SOIC (DW) package with standard 0.300-inch body width, RoHS-compliant NiPdAu lead finish, and moisture sensitivity level (MSL) 1 - suitable for standard reflow assembly without dry-pack requirements.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal bus transceiver and register applications.

Compared with SN74HCT245N and CD74HCT541M96, CD74HCT646M96 uniquely combines 3-state transceiver action with dual-register storage and multiplexed data routing - making it irreplaceable in applications requiring synchronized bus handoff, glitch-free arbitration, or real-time + stored data selection within a single IC.

Availability

CD74HCT646M96 is available at Aetrix Electronics and suitable for industrial PLC backplanes, avionics data multiplexing, and legacy microcontroller bus expansion requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HCT646M96 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 decades of heritage in high-reliability logic families including the 74HCT series.

CD74HCT646M96 belongs to TI's HCT logic product line, engineered for TTL-compatible operation in industrial and military systems where robustness, wide temperature tolerance, and predictable timing are essential.

FAQ

What is the maximum clock frequency supported by CD74HCT646M96?

The CD74HCT646M96 supports a maximum clock frequency of 25 MHz over its full operating temperature range (–55°C to 125°C) when VCC = 4.5 V. At 25°C, typical fmax reaches 30 MHz under 50-pF load conditions. This rating applies specifically to CLKAB and CLKBA inputs and assumes proper setup/hold timing compliance per the datasheet's timing requirements.

Does CD74HCT646M96 require external pull-up resistors on control pins?

Yes - to ensure defined high-impedance state during power-up or brownout, OE must be tied to VCC through a pull-up resistor. TI specifies minimum resistance based on driver sink capability; a 10-kΩ resistor is commonly used. DIR, SAB, SBA, and clock inputs do not require pull-ups if actively driven, but unused inputs must be terminated to VCC or GND per SCBA004 guidelines.

Can CD74HCT646M96 operate with a 3.3-V supply?

No - CD74HCT646M96 is specified only for 4.5 V to 5.5 V operation. Its TTL-compatible input thresholds (VIH = 2 V, VIL = 0.8 V) and internal HCT logic structure are optimized for 5-V systems. For 3.3-V operation, consider the CD74HC646 variant (2–6 V range), though it lacks TTL input compatibility.

How many data bits does CD74HCT646M96 handle simultaneously?

CD74HCT646M96 handles eight data bits simultaneously on both the A bus (pins A1–A8) and B bus (pins B1–B8). Each bit channel includes independent D-type flip-flop storage, 3-state output driver, and multiplexed input path - enabling full byte-wide bidirectional data transfer and registration in a single 24-pin SOIC package.

What is the purpose of SAB and SBA pins on CD74HCT646M96?

SAB and SBA are select-control inputs that determine whether real-time (transparent) or stored data appears on the respective A or B bus outputs. When SAB = L, real-time B-bus data passes to A-bus outputs; when SAB = H, stored B-bus data is routed instead - independent of OE and DIR states, enabling flexible data routing without disrupting bus direction or output enable.