Texas Instruments CY74FCT399ATSOC

Overview

CY74FCT399ATSOC from Texas Instruments is a quad 2-input register IC used for synchronous data selection and latching in TTL-compatible digital systems. It features noninverted outputs, 7 ns propagation delay (tPLH/tPHL), 64 mA sink / 32 mA source drive strength, and operates across –40°C to +85°C. It selects four bits from two input sources (I0X/I1X) under common select (S) control and latches them on the rising edge of CP.

For engineers reviewing the CY74FCT399ATSOC datasheet, CY74FCT399ATSOC pinout, CY74FCT399ATSOC application, or CY74FCT399ATSOC equivalent, key selection considerations include its FCT-family compatibility, Ioff partial-power-down support, edge-rate controlled noise immunity, and SOIC-16 package with 1.27 mm pitch.

Technical Context

The CY74FCT399ATSOC implements four independent D-type flip-flop channels, each with dual data inputs (I0X, I1X) and a shared select (S) line that determines source routing. Its clock (CP) is edge-triggered on the low-to-high transition, requiring only 3.5 ns setup and 1 ns hold time for data inputs relative to CP.

It uses standard FCT CMOS circuitry with TTL-level input thresholds (VIL = 0.8 V, VIH = 2.0 V), 5 V supply operation (4.75–5.25 V), and integrated edge-rate control to suppress switching noise. The Ioff feature disables outputs when VCC = 0 V, limiting backflow current to ±1 µA - enabling safe partial-power-down in mixed-supply systems.

Key Specifications

Pinout & Package

Package: SOIC-16 (DW), 7.5 mm × 10.3 mm body, 1.27 mm lead pitch, 2.65 mm max height, RoHS-compliant NIPDAU 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 CY74FCT399CTSOC, the CY74FCT399ATSOC trades 0.9 ns of speed margin for broader availability in tube packaging and slightly lower unit cost; versus SN74FCT399ATSOCT, it differs only in packaging format - both share identical timing, drive, and power-down behavior.

Availability

CY74FCT399ATSOC is available at Aetrix Electronics and suitable for industrial control bus multiplexing, legacy system data path switching, test equipment signal gating, and automated test fixture sequencing requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for CY74FCT399ATSOC 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 90 years of innovation in industrial, automotive, and communications markets.

The CY74FCT399ATSOC belongs to TI's FCT logic family, designed specifically for high-speed, low-noise, TTL-compatible 5 V digital interfacing in industrial and instrumentation applications where reliability and timing precision are critical.

FAQ

What is the maximum clock frequency supported by CY74FCT399ATSOC?

The CY74FCT399ATSOC does not specify a maximum clock frequency in its datasheet; instead, it defines timing via propagation delay (7 ns max) and minimum pulse width (5 ns for CP high/low). For reliable operation, the minimum clock period must exceed tPLH + tPHL + setup + hold - typically ≥18 ns, supporting up to ~55 MHz in ideal conditions. Actual usable frequency depends on board layout, load capacitance, and signal integrity.

Does CY74FCT399ATSOC support 3.3 V logic levels?

No, CY74FCT399ATSOC is a 5 V-only device with TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) and requires VCC = 4.75–5.25 V. It does not tolerate 3.3 V supply or guarantee correct operation with 3.3 V inputs. For mixed-voltage systems, level translation or a 3.3 V-compatible alternative like SN74LVC399A is required.

Is CY74FCT399ATSOC pin-compatible with CY74FCT399CTSOC?

Yes, CY74FCT399ATSOC and CY74FCT399CTSOC share identical SOIC-16 pinout, function table, and DC specifications. The only difference is AC performance: CY74FCT399CTSOC has 6.1 ns max propagation delay versus 7 ns for CY74FCT399ATSOC. They are drop-in replacements in most designs unless timing margins are constrained to <7 ns.

What is the purpose of the Ioff feature in CY74FCT399ATSOC?

The Ioff feature in CY74FCT399ATSOC disables all outputs when VCC = 0 V, limiting off-state leakage to ±1 µA. This prevents current backflow from live system buses into a powered-down section - essential for hot-swap capability, partial power-down modes, and safe power sequencing in multi-rail industrial systems using CY74FCT399ATSOC as a data path isolator.

Can CY74FCT399ATSOC drive LED indicators directly?

Yes, CY74FCT399ATSOC can drive LEDs directly in sink configuration: its 64 mA output sink current exceeds typical LED forward current (10–20 mA), and VOL ≤ 0.55 V at 64 mA ensures sufficient voltage headroom for series resistor calculation. For source-driving LEDs, its 32 mA source capability is also adequate - but verify VOH ≥ 2.4 V at load to maintain logic-high margin.