Texas Instruments CY74FCT138ATSOCT

Overview

CY74FCT138ATSOCT from Texas Instruments is a 1-of-8 active-low decoder IC with three binary address inputs (A0–A2), three enable inputs (E1, E2 low-active; E3 high-active), and eight mutually exclusive active-low outputs (O0–O7). It delivers 64-mA sink / 32-mA source drive, 5.8-ns max propagation delay, Ioff partial-power-down support, and TTL-compatible input/output logic levels. It is used in memory address decoding, peripheral selection, and bus demultiplexing in industrial control systems.

For engineers reviewing the CY74FCT138ATSOCT datasheet, CY74FCT138ATSOCT pinout, CY74FCT138ATSOCT application, or CY74FCT138ATSOCT equivalent, key selection criteria include output drive strength, enable logic configuration, Ioff capability for hot-swap compatibility, propagation delay consistency across enable and address paths, and SOIC-16 package suitability for legacy board layouts.

Technical Context

The CY74FCT138ATSOCT implements dual 1-of-8 decoding logic with three independent enables-two active-low (E1, E2) and one active-high (E3)-requiring all three to be asserted simultaneously for output activation. Its FCT-family architecture features edge-rate control circuitry to suppress switching noise and matched rise/fall times for clean signal transitions.

It supports partial-power-down via Ioff, which disables outputs and blocks reverse current when VCC = 0 V, enabling safe operation in mixed-voltage or hot-plug systems. All inputs tolerate TTL voltage levels (VIH = 2 V min, VIL = 0.8 V max), and outputs drive standard TTL loads with VOH ≥ 2.4 V (at –32 mA) and VOL ≤ 0.55 V (at 64 mA).

Key Specifications

Pinout & Package

Package: SOIC-16 (DW), 10.75 mm × 10.7 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 1-of-8 decoder applications.

Compared with SN74FCT138D and 74ACT138SCX, the CY74FCT138ATSOCT offers the optimal balance of moderate speed (5.8 ns), robust 64-mA drive, and Ioff-enabled power sequencing-making it preferred for industrial control and medical electronics where reliability under dynamic power conditions is critical.

Availability

CY74FCT138ATSOCT is available at Aetrix Electronics and suitable for memory address decoding, peripheral selection, and bus demultiplexing requiring stable component supply, long-term industrial lifecycle support, and RoHS-compliant SOIC packaging.

Supply support for CY74FCT138ATSOCT 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 industrial, automotive, and communications markets.

The CY74FCT138ATSOCT belongs to TI's FCT logic family, designed specifically for high-drive, noise-immune 5-V digital systems requiring TTL compatibility, predictable timing, and robust power sequencing behavior.

FAQ

What is the maximum propagation delay of the CY74FCT138ATSOCT?

The CY74FCT138ATSOCT has a maximum propagation delay of 5.8 ns for both address-to-output (A→O) and enable-to-output (E→O) paths, measured under recommended operating conditions (VCC = 4.75–5.25 V, TA = –40°C to 85°C). This value is guaranteed across temperature and voltage extremes, making it suitable for timing-critical decode applications in industrial control systems where deterministic latency is required.

Does the CY74FCT138ATSOCT support partial-power-down operation?

Yes, the CY74FCT138ATSOCT includes Ioff circuitry that disables all outputs and blocks reverse current flow when VCC = 0 V, enabling safe partial-power-down operation. This feature is critical in systems with hot-swap capability or multi-rail power sequencing, such as medical diagnostic equipment or programmable logic controllers, where unpowered sections must remain electrically isolated from active 5-V domains.

What are the enable input logic polarities for the CY74FCT138ATSOCT?

The CY74FCT138ATSOCT has three enable inputs: E1 and E2 are active-low, while E3 is active-high. All three must be asserted simultaneously (E1 = L, E2 = L, E3 = H) for any output to activate. This asymmetric enable structure supports flexible hierarchical decoding-e.g., using E3 to gate a group of decoders while E1/E2 provide local selection-enabling scalable 1-of-32 expansion with minimal external logic.

Can the CY74FCT138ATSOCT drive standard TTL loads directly?

Yes, the CY74FCT138ATSOCT is fully TTL-compatible: its inputs accept standard TTL voltage thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V), and its outputs deliver 64-mA sink / 32-mA source current-sufficient to drive up to 10 standard TTL inputs per output. This eliminates the need for buffer ICs in legacy 5-V systems, simplifying design and reducing bill-of-materials cost in applications like industrial HMIs and test instrumentation.

What package type and dimensions does the CY74FCT138ATSOCT use?

The CY74FCT138ATSOCT uses a SOIC-16 (DW) package: 10.75 mm × 10.7 mm body size, 1.27 mm lead pitch, with NiPdAu lead finish and MSL Level-1 rating (unlimited reflow). Its footprint matches industry-standard 5-V logic SOIC layouts, enabling drop-in replacement in existing designs-particularly valuable for sustaining engineering and obsolescence mitigation in aerospace and defense programs.