Texas Instruments SN74LV138ATDR

Overview

SN74LV138ATDR from Texas Instruments is a 3-line to 8-line decoder/demultiplexer IC designed for high-speed memory decoding and data routing. It operates from 4.5 V to 5.5 V, delivers max propagation delay of 7.6 ns at 5 V, supports partial-power-down via Ioff, and features TTL-voltage-compatible inputs. It is used in address decoding for SRAM/Flash systems where low-latency signal selection is critical.

For engineers reviewing the SN74LV138ATDR datasheet, SN74LV138ATDR pinout, SN74LV138ATDR application, or SN74LV138ATDR equivalent, key selection criteria include enable-input logic (G1 active-high, G2A/G2B active-low), output drive capability (±12 mA), Ioff protection for hot-swap scenarios, and SOIC-16 package compatibility with legacy board layouts.

Technical Context

The SN74LV138ATDR implements positive-logic 3-to-8 decoding with three binary select inputs (A, B, C) and three enable inputs (G1, G2A, G2B). Its function table defines eight active-low outputs (Y0–Y7), each asserted only when all enables are satisfied and the corresponding 3-bit address matches.

It integrates Ioff circuitry that disables outputs during power-down, preventing backflow current when VCC = 0 V while other supplies remain active. Input transition rate is specified at ≤20 ns/V, and output ground bounce (VOLP) remains <0.8 V at VCC = 5 V and TA = 25°C.

Key Specifications

Pinout & Package

SN74LV138ATDR is housed in a 16-pin SOIC (D) package, 7.5 mm × 10.3 mm body size, 1.75 mm max height, with 1.27 mm pitch and gull-wing leads. Pin 1 is located at the top-left corner with index marking.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV138ATDR, SN74HC138N lacks Ioff and delivers higher propagation delay, limiting use in hot-plug or high-speed systems; 74LVC138APW offers superior speed and density but sacrifices 5 V compatibility, requiring additional level-shifting circuitry in mixed-voltage environments.

Availability

SN74LV138ATDR is available at Aetrix Electronics and suitable for memory address decoding, peripheral selection, bus arbitration, and FPGA configuration interfaces requiring stable component supply across automotive, industrial, and computing applications.

Supply support for SN74LV138ATDR 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 founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial and automotive qualification.

The SN74LV138ATDR belongs to TI's LV logic family, engineered for 5 V systems requiring low power, high noise immunity, and robust Ioff protection in harsh operating environments.

FAQ

What is the maximum propagation delay of the SN74LV138ATDR at 5 V?

The SN74LV138ATDR has a maximum propagation delay (tpd) of 7.6 ns at VCC = 5 V, CL = 15 pF, and TA = 25°C. This value is measured from any address or enable input transition to the corresponding Yx output transition. At 125°C, the max tpd increases to 13 ns per the datasheet switching characteristics table. The SN74LV138ATDR maintains this performance across its full –40°C to +125°C operating range with appropriate layout decoupling.

Does the SN74LV138ATDR support partial-power-down mode?

Yes, the SN74LV138ATDR supports partial-power-down mode via its Ioff circuitry. When VCC = 0 V, the Ioff feature disables all outputs and limits reverse current to ≤5 µA, preventing damaging backflow from live buses into the unpowered device. This behavior is verified across the full –40°C to +125°C temperature range and is explicitly documented in the Electrical Characteristics table under the Ioff parameter.

What are the enable-input logic polarities for the SN74LV138ATDR?

The SN74LV138ATDR has three enable inputs: G1 is active-high, while G2A and G2B are both active-low. All three must be simultaneously asserted (G1 = high, G2A = low, G2B = low) for the decoder to operate. This mixed polarity reduces external gate count when expanding to larger decode trees - for example, a 24-line decoder can be built without any external inverters. The function table in the SN74LV138ATDR datasheet confirms this behavior across all operating conditions.

Can the SN74LV138ATDR interface directly with 3.3 V microcontrollers?

Yes, the SN74LV138ATDR accepts TTL-voltage-compatible inputs, meaning it recognizes VIH ≥ 2.0 V and VIL ≤ 0.8 V at VCC = 4.5–5.5 V. Since most 3.3 V microcontrollers output VOH ≥ 2.4 V and VOL ≤ 0.4 V, their signals meet these thresholds directly. No level shifter is needed. However, outputs remain 5 V referenced, so downstream 3.3 V devices must tolerate 5 V inputs or use clamping diodes per the SN74LV138ATDR absolute maximum ratings.

What package type is used for the SN74LV138ATDR orderable part number?

The SN74LV138ATDR uses the SOIC (D) package: 16-pin, 7.5 mm × 10.3 mm body, 1.27 mm lead pitch, gull-wing leads, and 1.75 mm max height. It is supplied in tape-and-reel format with 2500 units per reel. This package is footprint-compatible with legacy 74-series SOIC-16 devices and is documented in TI's DB0016A outline drawing. Thermal resistance θJA is 73°C/W, confirming suitability for natural-convection industrial PCB layouts.