Texas Instruments CY74FCT399CTQCT

Overview

CY74FCT399CTQCT from Texas Instruments is a high-speed quad 2-input register IC that selects four bits of data from either of two input sources (I0X/I1X) under control of a common select (S) input and latches them synchronously on the rising edge of clock (CP). It features noninverted outputs, 6.1 ns typical propagation delay, 64 mA sink / 32 mA source drive strength, Ioff partial-power-down support, and SOIC-16 packaging. It is used in bus multiplexing and data path selection within industrial control logic systems.

For engineers reviewing the CY74FCT399CTQCT datasheet, CY74FCT399CTQCT pinout, CY74FCT399CTQCT application, or CY74FCT399CTQCT equivalent, key selection criteria include its TTL-compatible input/output levels, matched rise/fall times for reduced EMI, edge-rate controlled switching, -40°C to 85°C operating range, and Ioff-enabled power sequencing in mixed-voltage systems.

Technical Context

The CY74FCT399CTQCT implements four independent D-type flip-flops, each with dual-data inputs (I0X, I1X) and a shared select (S) line to choose between sources. Its synchronous edge-triggered architecture requires only one setup time (3.5 ns) for data and 8.5 ns for S prior to CP's rising edge, with zero hold time for S and 1 ns for data.

It uses FCT-family silicon with reduced VOH (typically 3.3 V at IOH = –15 mA), edge-rate control circuitry to suppress noise, and Ioff protection enabling safe operation during partial power-down. All inputs tolerate TTL voltage levels, and outputs drive standard TTL loads with 64-mA sink capability.

Key Specifications

Pinout & Package

Package: SOIC-16 (DW), 7.5 mm × 10.3 mm body, 1.27 mm pitch, 2.65 mm max height, RoHS-compliant NiPdAu lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad 2-input register applications.

Compared with SN74FCT399CTSOCT and 74ACT399SCX, the CY74FCT399CTQCT uniquely combines Ioff protection, industrial temperature rating, and FCT-family compatibility-making it the only option among the three qualified for mixed-power-state designs requiring guaranteed isolation and noise-controlled edges.

Availability

CY74FCT399CTQCT is available at Aetrix Electronics and suitable for industrial control systems, legacy equipment upgrades, and bus arbitration circuits requiring stable component supply, long-term lifecycle support, and guaranteed SOIC-16 sourcing.

Supply support for CY74FCT399CTQCT 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 delivering analog, embedded processing, and logic solutions with emphasis on reliability, longevity, and industrial-grade qualification.

The CY74FCT399CTQCT belongs to TI's 74FCT logic family, engineered for high-speed, low-noise, TTL-compatible digital interfacing in mission-critical industrial and automotive subsystems.

FAQ

What is the maximum clock frequency supported by CY74FCT399CTQCT?

The CY74FCT399CTQCT does not specify a maximum clock frequency in its datasheet; instead, it guarantees timing performance via propagation delay (6.1 ns max) and minimum pulse width (5 ns for CP high/low). For reliable operation, the maximum usable frequency is determined by the sum of tPLH/tPHL and required setup/hold margins - typically supporting up to ~80 MHz in well-designed PCB layouts with proper termination and decoupling. The CY74FCT399CTQCT is optimized for synchronous bus control rather than high-frequency clock distribution.

Does CY74FCT399CTQCT support 3.3-V input logic levels?

No, the CY74FCT399CTQCT is designed for 5-V operation and requires TTL-compatible input thresholds: VIH ≥ 2.0 V and VIL ≤ 0.8 V. While its reduced VOH (3.3 V typical) eases interfacing with 3.3-V receivers, its inputs are not 3.3-V tolerant - applying 3.3-V logic signals directly may result in marginal or unreliable switching. For mixed-voltage systems, level-shifting or buffer conditioning is recommended before driving CY74FCT399CTQCT inputs.

Can CY74FCT399CTQCT be used in hot-swap applications?

Yes, the CY74FCT399CTQCT supports hot-swap operation via its Ioff feature: when VCC = 0 V, Ioff limits output leakage to ±1 µA, preventing damaging current backflow from live buses into the unpowered device. This allows safe insertion/removal in powered-backplane systems - provided all I/O lines are terminated and slew rates are controlled. The CY74FCT399CTQCT is explicitly characterized for partial-power-down use cases per its datasheet.

What is the meaning of "QCT" suffix in CY74FCT399CTQCT?

The "QCT" suffix in CY74FCT399CTQCT indicates a tape-and-reel packaged SOIC-16 variant with commercial temperature range (–40°C to +85°C), RoHS compliance, and NiPdAu lead finish. It corresponds to TI's orderable part number CY74FCT399CTSOCT, where "QCT" maps to "Tape and Reel, SOIC, 2000-unit reel". The CY74FCT399CTQCT is not a distinct silicon variant - it shares identical electrical specs, timing, and functionality with CY74FCT399CTSOC (tube version).

How does CY74FCT399CTQCT differ from CY74FCT399ATQCT?

The CY74FCT399CTQCT has a 6.1 ns maximum propagation delay, while the CY74FCT399ATQCT is slower at 7 ns max. Both share identical pinout, Ioff support, drive strength, and temperature range, but the "C" speed grade offers tighter timing for high-performance data path synchronization. The CY74FCT399CTQCT also exhibits lower dynamic current consumption (ICCD = 0.12 mA/MHz vs. 0.2 mA/MHz for "A"), making it preferable in power-constrained industrial modules where timing margin and efficiency are both critical.