Texas Instruments CY74FCT646TSOC

Overview

CY74FCT646TSOC from Texas Instruments is an 8-bit registered transceiver with 3-state outputs, designed for bidirectional data flow control between two TTL/CMOS buses. It features independent A/B registers, dual clock inputs (CPAB/CPBA), direction (DIR) and output-enable (G) controls, and delivers 64 mA sink / 32 mA source drive strength at 5 V. Used in bus isolation, data multiplexing, and register-controlled I/O expansion in industrial control backplanes.

For engineers reviewing the CY74FCT646TSOC datasheet, CY74FCT646TSOC pinout, CY74FCT646TSOC application, or CY74FCT646TSOC equivalent, key selection criteria include its 9 ns max propagation delay, Ioff partial-power-down support, matched rise/fall times, edge-rate controlled noise immunity, and SOIC-24 package compatibility with legacy FCT logic families.

Technical Context

The CY74FCT646TSOC implements a dual-bus architecture with separate D-type flip-flop registers for A and B buses, enabling simultaneous storage and selective multiplexing of real-time or registered data via SAB/SBA select inputs. Its DIR and G inputs jointly determine transceiver mode (A↔B), isolation mode (G high), or register-load mode (clock-triggered on CPAB↑/CPBA↑).

It integrates edge-rate control circuitry to suppress switching noise, supports Ioff for safe partial-power-down operation, and maintains full TTL-level input/output compatibility while operating from 4.75–5.25 V. The device exhibits matched tPLH/tPHL (1.5–9 ns) and low skew across all 8 channels under load.

Key Specifications

Pinout & Package

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

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74FCT646ATSOCT and 74ACT646SCX, the CY74FCT646TSOC provides optimal trade-off of noise-immune edge control, robust Ioff protection, and industrial temperature range - making it the preferred choice for bus-isolated, field-deployable systems requiring long-term reliability and mixed-power sequencing.

Availability

CY74FCT646TSOC is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy bus bridging, programmable I/O expansion, and real-time data capture systems requiring stable component supply, long lifecycle support, and traceable sourcing.

Supply support for CY74FCT646TSOC 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.

The CY74FCT646TSOC belongs to TI's FCT logic portfolio - engineered for noise-resilient, TTL-compatible bus interfacing in industrial, telecom, and computing infrastructure where signal integrity and power sequencing robustness are essential.

FAQ

What is the maximum clock frequency supported by CY74FCT646TSOC?

CY74FCT646TSOC does not specify a maximum clock frequency in its datasheet; instead, it defines minimum pulse width (tw ≥ 6 ns) and setup/hold times (tsu ≥ 4 ns, th ≥ 2 ns). These parameters support reliable operation up to approximately 83 MHz for register loading, assuming clean signal edges and proper layout. For transceiver mode (transparent path), propagation delay (1.5–9 ns) governs maximum data rate - typically usable in 100 MHz bus systems with timing margin. Always verify timing closure using worst-case values from the datasheet.

Does CY74FCT646TSOC support hot-swap or partial-power-down operation?

Yes, CY74FCT646TSOC supports partial-power-down via its Ioff feature. When VCC = 0 V, the outputs are actively disabled and leakage is limited to ±1 µA (per Ioff spec), preventing damaging current backflow from live buses. This allows safe insertion/removal in powered-backplane systems. However, note that Ioff only protects outputs - inputs remain functional and must be externally clamped or terminated if driven while unpowered.

What is the difference between CY74FCT646TSOC and CY74FCT646ATSOCT?

CY74FCT646TSOC has a 9 ns maximum propagation delay and is rated for 5.4 ns typical clock-to-output timing, while CY74FCT646ATSOCT improves this to 6.3 ns max and 4.5 ns typical - offering tighter timing margins. Both share identical SOIC-24 packaging, Ioff support, drive strength (64 mA sink/32 mA source), and operating temperature (–40°C to +85°C). The "A" suffix denotes enhanced speed grade; otherwise, they are pin- and function-compatible replacements.

Can CY74FCT646TSOC operate with a 3.3 V supply?

No, CY74FCT646TSOC is specified only for 4.75–5.25 V operation. Its input thresholds (VIH = 2 V min, VIL = 0.8 V max) and output drive characteristics are optimized for 5 V TTL compatibility. Applying 3.3 V will result in undefined logic behavior, insufficient noise margin, and failure to meet output voltage specifications (VOH ≥ 2.4 V, VOL ≤ 0.55 V). For 3.3 V systems, consider TI's LVC or ALVC families instead.

How does the SAB/SBA select logic work in CY74FCT646TSOC?

In CY74FCT646TSOC, SAB controls data source selection on the B→A path: when SAB = L, real-time B-bus data appears on A outputs; when SAB = H, stored B-register data appears. Similarly, SBA selects A→B path source: SBA = L enables real-time A data, SBA = H enables stored A-register data. Both inputs operate independently, allowing mixed-mode operation - e.g., real-time A to B while delivering stored B to A - enabling flexible data routing without external logic.