Texas Instruments SN74LVC138AD

Overview

SN74LVC138AD from Texas Instruments is a 3-line to 8-line decoder/demultiplexer in SOIC-16 package, operating from 1.65 V to 3.6 V with 5.8 ns max propagation delay at 3.3 V. It features three binary select inputs (A, B, C), two active-low enables (G2A, G2B), one active-high enable (G1), and eight active-low outputs (Y0–Y7). It is used for memory decoding, LED matrix column selection, and data routing in industrial control and embedded systems.

For engineers reviewing the SN74LVC138AD datasheet, SN74LVC138AD pinout, SN74LVC138AD application, or SN74LVC138AD equivalent, key selection criteria include its 1.65–3.6 V supply range, 5.5 V-tolerant inputs, low propagation delay, active-low output logic, and SOIC-16 footprint compatibility with legacy LVC-family layouts.

Technical Context

The SN74LVC138AD implements combinational logic decoding where binary inputs A, B, C determine which of eight outputs is driven LOW while all others remain HIGH-only when all three enables (G1 = HIGH, G2A = G2B = LOW) are simultaneously asserted. Its enable architecture supports cascading for larger decode trees without external inverters.

It uses advanced CMOS technology enabling 5.5 V-tolerant inputs while operating from as low as 1.65 V, making it suitable for mixed-voltage interfacing between 3.3 V controllers and 5 V peripherals. Output drive strength is ±24 mA at 3 V, with ground bounce (VOLP) < 0.8 V and undershoot (VOHV) > 2 V at 3.3 V, ensuring signal integrity in fast-switching applications.

Key Specifications

Pinout & Package

SN74LVC138AD is packaged in a 16-pin SOIC (D package), body size 9.90 mm × 3.91 mm, with standard 1.27 mm pitch. Pin numbering follows JEDEC MS-012, with pin 1 at top-left corner (notch or dot indicator).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC138N and 74LVT138PW, SN74LVC138AD uniquely balances ultra-low voltage operation (1.65 V), 5.5 V input tolerance, and sub-6 ns delay-making it optimal for modern mixed-supply embedded systems where flexibility and speed are jointly critical.

Availability

SN74LVC138AD is available at Aetrix Electronics and suitable for industrial control, LED display systems, and memory expansion applications requiring stable component supply, long-term manufacturability, and RoHS-compliant packaging.

Supply support for SN74LVC138AD 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 connectivity technologies, with decades of experience in logic IC design and industrial-grade qualification.

The SN74LVC138AD belongs to TI's LVC (Low-Voltage CMOS) logic family, engineered for low-power, high-speed operation across 1.65–3.6 V supplies-targeting portable, battery-powered, and mixed-voltage embedded systems.

FAQ

What is the maximum operating frequency supported by SN74LVC138AD?

SN74LVC138AD does not specify a maximum clock frequency because it is a combinational logic device-not clocked. Its usable switching rate is determined by propagation delay: at 3.3 V, tpd ≤ 5.8 ns implies reliable operation up to ~170 MHz toggle rate on enable or select inputs. System-level timing depends on load capacitance and drive strength, so keep trace lengths short and CL ≤ 50 pF for guaranteed performance.

Can SN74LVC138AD safely interface with 5 V microcontrollers?

Yes, SN74LVC138AD accepts input voltages up to 5.5 V regardless of VCC setting (1.65–3.6 V), making it safe for direct connection to 5 V GPIOs. Inputs are overvoltage-tolerant without external resistors or clamps. However, outputs swing from GND to VCC, so 5 V peripherals reading SN74LVC138AD outputs require level translation unless they accept TTL/CMOS thresholds at lower VCC.

How many SN74LVC138AD devices are needed to decode a 5-bit address into 32 outputs?

Two SN74LVC138AD devices are required to implement a 5-to-32 line decoder. Use the upper two address bits (A4,A3) to control the enable inputs of two SN74LVC138AD units-one enabled for A4A3 = 00, 01, 10, 11-and the lower three bits (A2,A1,A0) as common select inputs. This configuration requires no external inverters and maintains full active-low output consistency across all 32 lines.

Does SN74LVC138AD support hot-swap or live-insertion?

SN74LVC138AD is not specifically qualified for hot-swap operation. While its 2000 V HBM ESD rating and latch-up immunity (>250 mA) improve robustness, uncontrolled power sequencing during insertion can cause bus contention or supply transients. For hot-swap applications, use external power supervisors, slew-rate limited enable sequencing, and series current-limiting resistors on inputs/outputs-verified per system-level stress testing.

What is the recommended bypass capacitor for SN74LVC138AD?

A 0.1 µF ceramic capacitor placed as close as possible (<3 mm) to the VCC pin (pin 16) and GND pin (pin 8) is mandatory for stable operation. For systems with high-frequency noise or shared power rails, add a parallel 1 µF X7R ceramic capacitor. Avoid electrolytic or tantalum types due to higher ESL; ensure capacitor voltage rating exceeds VCC by ≥50% (e.g., 6.3 V for 3.3 V operation).