Texas Instruments CY74FCT138CTSOCT

Overview

CY74FCT138CTSOCT 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 strength, 5-ns propagation delay (max), and operates across –40°C to +85°C. It is used in memory address decoding and peripheral selection in industrial control logic systems.

For engineers reviewing the CY74FCT138CTSOCT datasheet, CY74FCT138CTSOCT pinout, CY74FCT138CTSOCT application, or CY74FCT138CTSOCT equivalent, key selection criteria include its TTL-compatible input thresholds, Ioff partial-power-down support, matched rise/fall times, and SOIC-16 package compatibility with legacy FCT logic families.

Technical Context

The CY74FCT138CTSOCT implements dual 1-of-8 decoding logic with three independent enables (E1/E2 low, E3 high) enabling cascaded expansion to 1-of-32 decoding using only four devices and one inverter. Its edge-rate control circuitry suppresses switching noise while maintaining full TTL-level compatibility on both inputs and outputs.

It features Ioff circuitry that disables outputs during power-down to prevent backflow current, and supports operation at VCC = 4.75 V to 5.25 V. All outputs are high-impedance unless E1 = L, E2 = L, and E3 = H - a strict combinational enable condition verified in the function table.

Key Specifications

Pinout & Package

CY74FCT138CTSOCT is housed in a 16-pin SOIC (SO) package per TI's DW drawing, with 1.27-mm pitch, 10.3-mm body width, and RoHS-compliant NiPdAu lead finish.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 1-of-8 decoder applications.

Compared with CY74FCT138ATSOCT, the CY74FCT138CTSOCT offers tighter 5-ns timing for higher-frequency bus decoding; compared with SN74F138N, it adds Ioff protection, edge-rate control, and surface-mount SOIC packaging - essential for modern industrial and automotive control modules.

Availability

CY74FCT138CTSOCT is available at Aetrix Electronics and suitable for memory address decoding, peripheral selection, bus arbitration, and digital panel interface applications requiring stable component supply, long-term industrial lifecycle support, and RoHS-compliant sourcing.

Supply support for CY74FCT138CTSOCT 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The CY74FCT138CTSOCT belongs to TI's FCT logic family, designed specifically for high-speed, low-noise, TTL-compatible digital interfacing in commercial and industrial systems where reliability, timing precision, and power-down safety are critical.

FAQ

What is the maximum propagation delay of the CY74FCT138CTSOCT under recommended operating conditions?

The CY74FCT138CTSOCT has a maximum propagation delay of 5 ns from any address (A0–A2) or enable (E1, E2, E3) input to any output (O0–O7), measured at VCC = 4.75 V to 5.25 V and TA = –40°C to +85°C. This value is specified in the switching characteristics table for the "CY74FCT138CT" speed grade and applies uniformly across all input-to-output paths.

Does the CY74FCT138CTSOCT support partial power-down, and how is it implemented?

Yes, the CY74FCT138CTSOCT supports partial power-down via its Ioff circuitry. When VCC = 0 V, the outputs are disabled and leakage is limited to ±1 µA even if driven to 4.5 V, preventing damaging backflow current. This feature is explicitly tested and guaranteed in the electrical characteristics table and enables safe use in hot-pluggable or modular power-rail architectures.

What are the voltage thresholds for logic-high and logic-low inputs on the CY74FCT138CTSOCT?

The CY74FCT138CTSOCT specifies VIH = 2.0 V (minimum) and VIL = 0.8 V (maximum) across its operating temperature range. These thresholds ensure full compatibility with standard TTL logic families and allow direct interfacing with 5-V microcontrollers, FPGAs, and legacy bus drivers without level translation.

Can the CY74FCT138CTSOCT be used to build a 1-of-32 decoder, and what additional components are required?

Yes, the CY74FCT138CTSOCT can be used to construct a 1-of-32 decoder. The datasheet confirms this is achievable using four CY74FCT138CTSOCT devices and one inverter. Two address bits select which decoder is active via E3, while the remaining three bits (A0–A2) select the specific output within that decoder - all with no external combinational logic beyond the inverter.

Is the CY74FCT138CTSOCT pin-compatible with earlier FCT-series decoders such as the CY74FCT138T?

Yes, the CY74FCT138CTSOCT is functionally and pinout-compatible with CY74FCT138T variants in the same SOIC-16 package. Both share identical pin assignments (A0–A2, E1–E3, O0–O7, VCC, GND), enable logic, truth table, and DC specifications - differing only in propagation delay (5 ns vs 9 ns) and dynamic current consumption.