Texas Instruments CY74FCT821CTQCT

Overview

CY74FCT821CTQCT from Texas Instruments is a 10-bit positive-edge-triggered bus-interface register with 3-state outputs, designed for high-capacitance load drive (64 mA sink / 32 mA source), TTL-compatible I/O levels, and partial-power-down support via I_off. It operates at 5 V (4.75–5.25 V), delivers 6 ns propagation delay (t_PLH/t_PHL), and is used in address/data bus buffering for industrial control and legacy computing systems.

For engineers reviewing the CY74FCT821CTQCT datasheet, CY74FCT821CTQCT pinout, CY74FCT821CTQCT application, or CY74FCT821CTQCT equivalent, key selection criteria include its QSOP-24 package, edge-rate controlled outputs for noise immunity, matched rise/fall times, and I_off-enabled power-down isolation in mixed-voltage or hot-swap environments.

Technical Context

This device implements ten independent D-type flip-flops clocked on the low-to-high transition of CP, with synchronous 3-state output control via OE. Its logic architecture supports true register functionality-not latching-enabling precise timing alignment in parallel data paths.

Edge-rate control circuitry actively limits slew rate to reduce simultaneous switching noise, while I_off disables all outputs when V_CC = 0 V, preventing backflow current during partial power-down. Input thresholds (V_IL = 0.8 V, V_IH = 2.0 V) and output drive (V_OH = 2.4 V min @ –15 mA, V_OL = 0.55 V max @ 64 mA) ensure robust TTL interoperability.

Key Specifications

Pinout & Package

Package: SSOP-24 (DBQ), 5.3 mm × 7.2 mm body, 0.635 mm pitch, RoHS-compliant NIPDAU finish, MSL Level-2 (260°C, 1 year).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar bus-interface register applications.

Compared with CY74FCT821CTQCT, the SOIC variant offers easier hand-soldering but lower density and higher thermal impedance, while the SN74FCT821CTSOCT is a direct material-equivalent with identical performance and layout requirements - making it suitable for BOM flexibility without design change.

Availability

CY74FCT821CTQCT is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy computer bus expansion, and automotive body control modules requiring stable component supply, long-lifecycle support, and RoHS-compliant SSOP packaging.

Supply support for CY74FCT821CTQCT 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 50 years of innovation in high-reliability interface and timing products.

CY74FCT821CTQCT belongs to the 74FCT family of fast CMOS logic devices engineered for TTL-compatible operation in industrial and computing infrastructure - emphasizing noise immunity, power-down safety, and bus-loading efficiency.

FAQ

What is the maximum clock frequency supported by CY74FCT821CTQCT?

CY74FCT821CTQCT does not specify a maximum clock frequency in its datasheet. Instead, timing is defined by minimum pulse width (t_w = 6 ns) and setup/hold times (t_su = 3 ns, t_th = 1.5 ns). For reliable operation, the maximum usable clock frequency depends on system-level timing margins but typically supports up to ~125 MHz in well-designed 50-pF load environments. Always verify against actual board trace capacitance and driver strength when deploying CY74FCT821CTQCT.

Does CY74FCT821CTQCT support hot-swap or live-insertion applications?

Yes, CY74FCT821CTQCT supports partial-power-down operation via its I_off feature. When V_CC = 0 V, I_off limits output leakage to ±1 µA, preventing damaging back-current flow into powered sections of the bus. This makes CY74FCT821CTQCT suitable for hot-swap backplane interfaces - provided OE is held inactive (high) during insertion and V_CC ramp-up is controlled per TI's recommended power sequencing guidelines.

What is the meaning of "FCT821C" marking on CY74FCT821CTQCT?

"FCT821C" is the top-side marking laser-etched on CY74FCT821CTQCT, indicating its speed grade (C = 6 ns propagation delay), logic family (FCT), and function (821 = 10-bit bus-interface register). This marking aligns with TI's standardized identification scheme and appears consistently across all CY74FCT821CT variants - including SOIC and QSOP packages - confirming functional and timing equivalence for CY74FCT821CTQCT.

Can CY74FCT821CTQCT drive 50 Ω transmission lines directly?

No, CY74FCT821CTQCT is not designed for direct 50 Ω transmission line driving. Its output structure targets bus loading (typ. 9–12 pF output capacitance, 64 mA sink) rather than RF impedance matching. Driving 50 Ω lines would cause severe reflections and overshoot. For such applications, use dedicated line drivers or add series termination (e.g., 33 Ω resistor) close to the CY74FCT821CTQCT output pin to dampen edge rates and improve signal integrity.

How does the edge-rate control in CY74FCT821CTQCT improve noise performance?

CY74FCT821CTQCT integrates on-die edge-rate control that intentionally limits output dV/dt, reducing simultaneous switching noise (SSN) and ground bounce. This results in lower broadband EMI emissions and improved signal integrity on shared buses - especially critical in dense layouts with multiple parallel outputs switching synchronously. Measured improvements include >10 dB reduction in peak radiated emissions compared to non-edge-controlled FCT variants, directly benefiting CY74FCT821CTQCT deployment in noise-sensitive industrial enclosures.