Texas Instruments CD74ACT138BQBR

Overview

CD74ACT138BQBR from Texas Instruments is a high-speed 3-line-to-8-line decoder/demultiplexer in a 16-pin WQFN package, operating at 4.5–5.5 V with ±24 mA output drive, 3.1 ns typical propagation delay (t_PLH/t_PHL), and TTL-compatible inputs-designed for memory decoding and data routing in industrial control and embedded systems.

For engineers reviewing the CD74ACT138BQBR datasheet, CD74ACT138BQBR pinout, CD74ACT138BQBR application, or CD74ACT138BQBR equivalent, key selection criteria include its triple enable architecture (G1, G2A, G2B), balanced propagation delays, SCR-latchup-resistant CMOS process, 2 kV HBM ESD rating, and compatibility with high-speed memory subsystems requiring low-latency address decoding.

Technical Context

The CD74ACT138BQBR implements positive-logic 3-to-8 decoding with three independent enable inputs: one active-high (G1) and two active-low (G2A, G2B), enabling flexible cascading without external inverters. Its function table defines eight mutually exclusive active-low outputs (Y0–Y7), where only one output goes low per valid input combination when all enables are asserted.

It operates across –55°C to +125°C using a radiation-hardened, SCR-latchup-resistant CMOS process, supports TTL-level input thresholds (V_IL = 0.8 V, V_VIH = 2.0 V), and delivers rail-to-rail output swing with guaranteed VOL ≤ 0.44 V at I_OL = 24 mA and VOH ≥ 3.8 V at I_OH = –24 mA under recommended conditions.

Key Specifications

Pinout & Package

CD74ACT138BQBR uses a 16-pin WQFN (BQB) package measuring 3.5 mm × 2.5 mm with 0.5 mm pitch and an exposed thermal pad. The package requires soldering the thermal pad to PCB ground for optimal thermal performance and mechanical reliability.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3-to-8 decoder applications.

Compared with SN74ACT138PWR and 74LCX138MTCX, the CD74ACT138BQBR uniquely combines 5-V TTL compatibility, extended temperature range (–55°C to +125°C), superior thermal performance via exposed pad, and proven latchup immunity-making it the preferred choice for ruggedized memory and control subsystems.

Availability

CD74ACT138BQBR is available at Aetrix Electronics and suitable for industrial control systems, automotive body electronics, test equipment signal routing, and high-reliability memory subsystems requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74ACT138BQBR 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 decades of heritage in high-reliability logic families and industrial-grade qualification.

The CD74ACT138BQBR belongs to TI's advanced CMOS logic portfolio designed specifically for high-speed memory decoding and data-routing applications demanding minimal propagation delay, robust noise immunity, and extended temperature operation.

FAQ

What is the maximum operating temperature for CD74ACT138BQBR?

The CD74ACT138BQBR is fully specified and qualified for continuous operation from –55°C to +125°C. This extended temperature range is validated per TI's industrial qualification standards and supports deployment in under-hood automotive, industrial motor drives, and outdoor infrastructure equipment where ambient temperatures exceed commercial limits. The WQFN package's thermal pad enhances heat transfer to the PCB, sustaining performance at upper-range junction temperatures.

Does CD74ACT138BQBR support TTL-level inputs directly?

Yes, CD74ACT138BQBR features TTL-voltage compatible inputs, meaning it accepts standard TTL logic thresholds: V_IL ≤ 0.8 V (guaranteed LOW) and V_VIH ≥ 2.0 V (guaranteed HIGH) across its full operating temperature range. No external level-shifting circuitry is required when interfacing with legacy 5-V TTL microcontrollers, FPGAs, or discrete logic families-reducing bill-of-materials cost and layout complexity.

How many enable inputs does CD74ACT138BQBR have, and what are their polarities?

The CD74ACT138BQBR has three enable inputs: G1 (active-high), G2A (active-low), and G2B (active-low). All three must be simultaneously asserted-G1 = HIGH, G2A = LOW, G2B = LOW-for the decoder to operate. This configuration allows hierarchical expansion (e.g., building 24- or 32-line decoders) without external inverters, simplifying system-level logic design and improving timing predictability.

What is the output drive capability of CD74ACT138BQBR?

The CD74ACT138BQBR provides ±24 mA output drive per pin, enabling direct interfacing with multiple F-series logic loads (fanout to 15 F devices) or 50-Ω transmission lines. At I_OL = 24 mA, VOL remains ≤ 0.44 V (–40°C to +85°C); at I_OH = –24 mA, VOH stays ≥ 3.8 V. This robust drive strength ensures signal integrity in noisy industrial environments and supports longer trace routing without buffering.

Is CD74ACT138BQBR latchup-resistant, and what standard does it meet?

Yes, CD74ACT138BQBR employs a SCR-latchup-resistant CMOS process and circuit design, tested and qualified to exceed 2 kV ESD protection per MIL-STD-883, Method 3015 (Human Body Model). This makes it highly resilient against latchup events caused by voltage transients, ESD discharge, or supply rail disturbances-critical for use in factory automation, power electronics controls, and other electrically harsh settings where reliability is non-negotiable.