Texas Instruments SN74HC138NS

Overview

SN74HC138NS from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in SO (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 SN74HC138NS datasheet, SN74HC138NS pinout, SN74HC138NS application, or SN74HC138NS equivalent, this device serves as a high-speed memory decoder, data router, or cascaded enable-controlled demultiplexer in industrial control, server address decoding, and white goods logic subsystems.

Technical Context

The SN74HC138NS implements combinational 3-to-8 decoding with three binary select inputs (A, B, C), two active-low enables (G2A, G2B), and one active-high enable (G1). All eight outputs are active-low and mutually exclusive - only one output asserts LOW per valid input combination when all enables are satisfied.

It uses standard CMOS logic with balanced output drive, supports cascading via enable inputs without external inverters, and features low input current (≤1 µA max) and low quiescent ICC (≤80 µA max), making it suitable for battery-sensitive or thermally constrained embedded systems.

Key Specifications

Pinout & Package

SN74HC138NS is housed in a 16-pin SO (Small Outline) package with gull-wing leads, 10.20 mm × 5.30 mm body size, and standard JEDEC MO-012AC footprint. Pin numbering follows top-view orientation with Pin 1 at bottom-left corner.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT138N and 74LV138PW, SN74HC138NS provides the broadest supply range (2–6 V), widest industrial temperature support (–40 °C to +85 °C), and proven reliability in legacy and mixed-voltage systems - making it the default choice unless TTL compatibility or ultra-low-voltage operation is mandatory.

Availability

SN74HC138NS is available at Aetrix Electronics and suitable for LED matrix displays, server memory decoding, and white goods control systems requiring stable component supply, long-term industrial lifecycle support, and RoHS-compliant sourcing.

Supply support for SN74HC138NS 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 expertise in high-reliability industrial and automotive components.

The SN74HC138NS belongs to TI's 74HC logic family, designed for high-speed, low-power combinatorial decoding in memory systems, data routing, and industrial control - balancing performance, power efficiency, and robustness across wide voltage and temperature ranges.

FAQ

What is the maximum operating voltage for SN74HC138NS?

The SN74HC138NS supports a supply voltage range of 2 V to 6 V, with absolute maximum rating of 7 V. Operation above 6 V risks exceeding recommended conditions and may degrade reliability or cause functional failure. For sustained 5 V or 3.3 V designs, SN74HC138NS delivers full specification compliance including propagation delay, drive strength, and input thresholds.

Does SN74HC138NS support cascading for larger decoder configurations?

Yes, SN74HC138NS supports cascading via its three enable inputs (G1, G2A, G2B). Two active-low enables and one active-high enable allow direct connection between multiple devices - for example, two SN74HC138NS units can implement a 24-line decoder without external inverters, and a third can extend to 32 lines with only one inverter. This architecture eliminates glue logic and preserves timing integrity.

Can SN74HC138NS directly drive LEDs in a matrix display?

Yes, SN74HC138NS can directly sink LED column current due to its active-low outputs and ±4-mA drive capability at 5 V. Each Yx output pulls LOW to enable one column while remaining outputs stay HIGH, ensuring only one column is active per decode cycle. This eliminates external N-channel switches in common-cathode matrices, provided per-output current stays within 4 mA and total package power dissipation is managed.

What is the thermal resistance (RθJA) of SN74HC138NS in its SO package?

The junction-to-ambient thermal resistance (RθJA) for SN74HC138NS in the SO (16) package is 91.1 °C/W, per TI's SCLS107G datasheet revision G. This value assumes standard JEDEC 2-layer board layout; actual thermal performance improves with copper pour, thermal vias, or forced airflow. For continuous operation near 80 µA ICC, self-heating remains negligible under typical ambient conditions.

Is SN74HC138NS pin-compatible with other 74xx138 variants?

SN74HC138NS shares identical pinout and function with all 16-pin 74xx138 variants in D (SOIC), DB (SSOP), N (PDIP), PW (TSSOP), J (CDIP), and W (CFP) packages - including SN74HC138D, SN74HC138DB, and SN74HC138N. The only differences are package dimensions, thermal characteristics, and moisture sensitivity level; electrical behavior and logic function are fully interchangeable.