Texas Instruments SN74HC138D

Overview

SN74HC138D from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in SOIC-16 package, operating from 2 V to 6 V, with typical propagation delay of 15 ns at 6 V, ±4-mA output drive at 5 V, and active-low outputs enabling direct LED column sinking in matrix displays.

For engineers reviewing the SN74HC138D datasheet, SN74HC138D pinout, SN74HC138D application, or SN74HC138D equivalent, this device serves as a high-speed memory decoder, address demultiplexer, or low-side LED driver where precise 3-bit binary selection and cascading via three enable inputs (G1, G2A, G2B) are required.

Technical Context

The SN74HC138D implements combinational logic decoding using CMOS technology, accepting three binary inputs (A, B, C) to assert exactly one of eight active-low outputs (Y0–Y7). Its functional mode depends on simultaneous assertion of one high-enable (G1) and two low-enables (G2A, G2B), with all outputs forced high if any enable is inactive.

Propagation delay is supply-voltage dependent - 38 ns max at 6 V, 45 ns at 4.5 V - and output transition times remain under 16 ns (VCC = 6 V). Input leakage stays below 1 µA, and ICC remains ≤80 µA across temperature and voltage, supporting low-power system-level decoding without timing bottlenecks.

Key Specifications

Pinout & Package

SN74HC138D uses a 16-pin SOIC (Small Outline Integrated Circuit) package measuring 9.90 mm × 3.90 mm, with standard 1.27-mm pitch and gull-wing leads compatible with automated SMT assembly and IPC-7351B footprint requirements.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT138D and 74LCX138MTCX, the SN74HC138D offers broader supply flexibility (2–6 V) and industrial temperature support (–40 °C to +85 °C), making it optimal for general-purpose decoding where voltage agility and environmental robustness outweigh ultra-low-delay or TTL-compatibility needs.

Availability

SN74HC138D is available at Aetrix Electronics and suitable for LED matrix displays, memory address decoding, and industrial I/O expansion requiring stable component supply across automotive, factory automation, and building management systems.

Supply support for SN74HC138D 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 ICs, with decades of heritage in industry-standard logic families.

The SN74HC138D belongs to TI's HC (High-Speed CMOS) logic family, designed for low-power, high-noise-immunity digital control and signal routing in industrial, computing, and consumer electronics.

FAQ

What is the maximum propagation delay of SN74HC138D at 5 V supply?

The maximum propagation delay of SN74HC138D from input (A/B/C or enable) to any output (Y0–Y7) is 45 ns at VCC = 4.5 V and TA = –40 °C to +85 °C, per Section 6.10 of the official datasheet. This value ensures compatibility with 22 MHz address bus timing in memory systems.

Can SN74HC138D drive LEDs directly without current-limiting resistors?

No - SN74HC138D cannot drive LEDs directly without external current-limiting resistors. While its outputs can sink up to 4 mA at 5 V, LED forward voltage and desired brightness require series resistance to set safe current; omitting it risks exceeding absolute max output current (±25 mA) and damaging the SN74HC138D.

How many enable inputs does SN74HC138D have, and what are their logic polarities?

SN74HC138D 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 normal decoding operation; any violation forces all Y0–Y7 outputs HIGH.

Is SN74HC138D RoHS compliant and lead-free?

Yes - SN74HC138D variants such as SN74HC138DRG4.A are RoHS compliant and feature lead-free terminations (NIPDAU finish), with MSL Level-1 rating and peak reflow tolerance up to 260 °C, meeting JEDEC J-STD-020 standards for surface-mount assembly.

What is the recommended bypass capacitor for SN74HC138D?

Texas Instruments recommends a 0.1-µF ceramic bypass capacitor placed as close as possible to the VCC (Pin 16) and GND (Pin 8) pins of SN74HC138D. For enhanced high-frequency noise suppression, a parallel 1-µF capacitor may be added, but the 0.1-µF unit must be nearest the IC power pins.