Texas Instruments CY74FCT646CTSOCT

Overview

CY74FCT646CTSOCT from Texas Instruments is an 8-bit registered transceiver with 3-state outputs, designed for bidirectional data routing between A and B buses in TTL- and FCT-compatible digital systems. It features independent A/B registers, dual clock inputs (CPAB/CPBA), direction control (DIR), output-enable (G), and data-source-select inputs (SAB/SBA). Key confirmed specs include 5.4 ns max propagation delay, 64 mA sink / 32 mA source drive strength, and operation across –40°C to +85°C.

For engineers reviewing the CY74FCT646CTSOCT datasheet, CY74FCT646CTSOCT pinout, CY74FCT646CTSOCT application, or CY74FCT646CTSOCT equivalent, this device is selected for high-noise-margin bus interfacing in industrial control backplanes, legacy system upgrades requiring FCT-level timing and drive, and applications demanding partial-power-down support via Ioff.

Technical Context

The CY74FCT646CTSOCT implements a dual-register architecture with separate clock-pulse inputs (CPAB for A→B register, CPBA for B→A register), enabling asynchronous latching of data from either bus. Its transceiver supports real-time (transparent) and registered (latched) modes via SAB/SBA controls, with DIR determining active data flow direction when G is low.

It integrates edge-rate control circuitry to reduce switching noise, matched rise/fall times for clean signal integrity, and Ioff protection that disables outputs during power-down to prevent backflow current. Fully compatible with TTL input thresholds (VIH = 2 V, VIL = 0.8 V) and 5-V supply operation (4.75–5.25 V).

Key Specifications

Pinout & Package

Package: SOIC-24 (DW), 15.4 mm × 7.5 mm body, 1.27 mm pitch, RoHS-compliant NiPdAu lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CY74FCT646ATSOCT and SN74FCT646CTSOIC, the CY74FCT646CTSOCT delivers the fastest timing (5.4 ns), full industrial temperature support (–40°C to +85°C), and guaranteed Ioff behavior - making it the optimal choice for mission-critical industrial and telecom infrastructure.

Availability

CY74FCT646CTSOCT is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus extensions, and programmable logic I/O expansion requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for CY74FCT646CTSOCT 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 industry-standard logic families including FCT, LS, and AC.

The CY74FCT646CTSOCT belongs to TI's military- and industrial-grade FCT logic portfolio, engineered for robustness in harsh environments, precise timing control, and seamless interoperability with legacy TTL systems.

FAQ

What is the maximum operating frequency supported by CY74FCT646CTSOCT?

The CY74FCT646CTSOCT does not specify a maximum clock frequency in its datasheet; instead, it guarantees timing parameters such as 5.4 ns max propagation delay and 2 ns min pulse width. For reliable operation, system designers should ensure setup/hold times (tsu = 2 ns, th = 1.5 ns) and clock-to-output delays are met - supporting effective data rates up to ~185 MHz in well-designed PCB layouts with controlled impedance.

Does CY74FCT646CTSOCT support hot-swap or partial-power-down operation?

Yes, CY74FCT646CTSOCT includes Ioff circuitry that actively disables outputs when VCC = 0 V, limiting Ioff current to ±1 µA. This feature prevents damaging current backflow during hot-swap events or when the device is powered down while other system rails remain active - a key requirement for modular industrial controllers and telecom line cards.

How does the SAB and SBA control logic affect data routing in CY74FCT646CTSOCT?

In CY74FCT646CTSOCT, SAB selects whether A-bus output reflects real-time A data (SAB = L) or stored A-register data (SAB = H); similarly, SBA selects real-time B data (SBA = L) or stored B-register data (SBA = H). These controls operate independently of DIR and G, enabling flexible multiplexing of live and latched data streams without changing direction or enable states.

Is CY74FCT646CTSOCT pin-compatible with older 74LS646 or 74F646 devices?

No, CY74FCT646CTSOCT is not pin-compatible with 74LS646 or 74F646. While functionally similar as 8-bit registered transceivers, the CY74FCT646CTSOCT uses a 24-pin SOIC package with dedicated CPAB/CPBA and SAB/SBA inputs, whereas 74LS646 uses a 24-pin DIP with different pin assignments (e.g., shared clock, no separate select lines). Direct replacement requires PCB redesign.

What thermal considerations apply to CY74FCT646CTSOCT in continuous operation?

CY74FCT646CTSOCT in SOIC-24 package has θJA = 46°C/W. At maximum specified IOL = 64 mA per output and worst-case 5.25 V supply, total power dissipation remains below 150 mW under typical loading. With proper PCB copper pour and ambient ≤ +85°C, junction temperature stays within safe limits; no heatsink is required for standard industrial use.