Texas Instruments SN74ALS158DR

Overview

SN74ALS158DR from Texas Instruments is a quad 2-line-to-1-line data selector/multiplexer with inverted output logic, designed for high-speed TTL-compatible digital systems. It features buffered inputs and outputs, a common strobe (G) enable, and selects one of two 4-bit data sources (A or B) to drive four inverted outputs (1Y–4Y). It operates from 0°C to 70°C with V_CC = 4.5–5.5 V and supports 50-pF load switching at ≤18 ns max propagation delay.

For engineers reviewing the SN74ALS158DR datasheet, SN74ALS158DR pinout, SN74ALS158DR application, or SN74ALS158DR equivalent, key selection considerations include its inverted-output architecture (vs. true-output SN74ALS157DR), ALS family propagation delay vs. AS variants, SOIC-16 package compatibility, and legacy TTL-level interface requirements in industrial control and retro-computing designs.

Technical Context

The SN74ALS158DR implements four independent 2:1 multiplexers sharing a single A/B select line and global strobe (G) enable. Each channel routes either the A or B input pair to its corresponding inverted output (e.g., 1A/1B → 1Y), with all outputs active-low when G = LOW. Its ALS logic ensures compatibility with standard TTL voltage thresholds while reducing power consumption versus earlier 74LS families.

Unlike the SN74ALS157DR, this device inverts output data-minimizing propagation delay by eliminating an external inverter stage. The SOIC-16 package (D suffix) uses standard 1.27-mm pitch, with pin 1 located in quadrant Q1 per TI tape-and-reel specifications, and supports reflow soldering per MSL Level-1 rating.

Key Specifications

Pinout & Package

SN74ALS158DR is supplied in a 16-pin SOIC (D) package measuring 10.4 mm × 5.3 mm × 2.0 mm max height, with 1.27-mm lead pitch and RoHS-compliant NiPdAu lead finish.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar data selector applications.

Compared with SN74ALS157DR and SN74AS158N, the SN74ALS158DR uniquely balances low-power ALS performance with inverted-output functionality in a surface-mount SOIC package-making it optimal for space-constrained, legacy-TTL-compatible systems requiring deterministic active-low data routing.

Availability

SN74ALS158DR is available at Aetrix Electronics and suitable for industrial control logic, retro computing bus interfaces, digital test equipment, and legacy instrumentation signal routing requiring stable component supply and long-term obsolescence management.

Supply support for SN74ALS158DR 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 U.S.-based semiconductor company founded in 1930, specializing in analog and embedded processing technologies with broad industrial, automotive, and consumer product portfolios.

The SN74ALS158DR belongs to TI's legacy 74ALS logic family, engineered for backward compatibility with TTL systems while delivering improved speed-power trade-offs for mid-1980s digital control and instrumentation applications.

FAQ

What logic family does the SN74ALS158DR belong to, and how does it differ from 74LS?

The SN74ALS158DR belongs to the advanced low-power Schottky (ALS) logic family. Compared to standard 74LS, it delivers approximately twice the switching speed (e.g., 10.5 ns max t_PHL vs. ~20 ns for 74LS158) while consuming roughly half the quiescent current (5 mA typical vs. ~10 mA). Its input thresholds and output drive remain fully compatible with TTL voltage levels, enabling drop-in replacement in most 74LS-based designs without redesign.

Does the SN74ALS158DR support 3-state outputs?

No, the SN74ALS158DR does not provide 3-state (high-impedance) outputs. Its outputs are push-pull totem-pole structures that drive either HIGH or LOW based on input states and strobe (G) control. When G = HIGH, all outputs are forced HIGH (not high-Z); only when G = LOW do they actively drive inverted data. For true 3-state operation, consider alternatives like SN74ALS257N.

What is the function of the A/B pin on the SN74ALS158DR?

The A/B pin is a common select control for all four multiplexer channels. When A/B = HIGH, inputs 1A–4A are routed to outputs 1Y–4Y (inverted); when A/B = LOW, inputs 1B–4B are selected instead. This enables synchronized 4-bit word selection between two parallel data sources using a single control line, critical for bus arbitration and dual-port memory interfacing.

Can the SN74ALS158DR operate at 3.3 V?

No, the SN74ALS158DR is not rated for 3.3-V operation. Its absolute maximum V_CC is 7 V, but recommended operating range is strictly 4.5 V to 5.5 V. At 3.3 V, input thresholds (V_IL = 0.8 V, V_IH = 2.0 V) would not be reliably met, and output drive capability collapses. For 3.3-V systems, consider modern equivalents such as SN74LVC157A or SN74AHC157.

How does the SN74ALS158DR handle unused inputs?

Unused inputs on the SN74ALS158DR-such as unconnected A or B lines-must be terminated to a defined logic level (V_CC or GND) to prevent floating nodes that cause excessive current draw and erratic switching. TI recommends tying unused data inputs to GND (for LOW) or V_CC via a 1-kΩ resistor (for HIGH); the strobe (G) and A/B pins should never be left floating, as they directly control output states of the SN74ALS158DR.