Texas Instruments SN74ALS157AD

Overview

SN74ALS157AD from Texas Instruments is a quad 2-line-to-1-line data selector/multiplexer in a 16-pin SOIC (D) package, operating from 4.5 V to 5.5 V over 0°C to 70°C. It routes one of two 4-bit input sources to four outputs under A/B select and strobe (G) control, delivering true (non-inverted) data with typical propagation delays of 9 ns (A/B→Y) and 14 ns (G→Y) at VCC = 5 V, CL = 50 pF.

For engineers reviewing the SN74ALS157AD datasheet, SN74ALS157AD pinout, SN74ALS157AD application, or SN74ALS157AD equivalent, this page provides verified functional behavior, validated timing under industrial temperature and load conditions, confirmed SOIC-D package dimensions and pin mapping, and direct alternative options for legacy TTL-compatible multiplexer upgrades.

Technical Context

The SN74ALS157AD implements four independent 2:1 multiplexers sharing a common A/B select line and individual enable (G) control per output group. Its ALS (Advanced Low-Power Schottky) logic family delivers TTL-compatible voltage thresholds (VIH = 2 V min, VIL = 0.8 V max) with reduced power consumption versus standard LS, while maintaining full 74-series pinout compatibility.

Each output features buffered drivers capable of sourcing −0.4 mA and sinking 4 mA (IOL = 4 mA min), supporting direct interfacing with other TTL/ALS loads without external pull-ups. The device contains no internal latches or memory-operation is purely combinational, with all outputs updating synchronously on input transitions.

Key Specifications

Pinout & Package

SN74ALS157AD uses a 16-pin Small-Outline Integrated Circuit (SOIC-D) package with 1.27 mm lead pitch and 7.5 mm × 10.3 mm body size. Pin 1 is located at the top-left corner with a beveled edge or dot marking.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad 2:1 multiplexer applications.

Compared with SN74ALS157AN and SN74AS157D, the SN74ALS157AD delivers the best compromise of surface-mount compatibility, moderate speed (9–14 ns), and low active power (6–11 mA), making it ideal for cost-sensitive, volume-produced commercial electronics requiring proven TTL interoperability.

Availability

SN74ALS157AD is available at Aetrix Electronics and suitable for microprocessor bus selection, industrial I/O expansion, legacy memory mapping, and test equipment signal routing requiring stable component supply and long-term obsolescence management.

Supply support for SN74ALS157AD 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 SN74ALS157AD belongs to TI's legacy 74ALS logic family, designed specifically for drop-in replacement of 74LS devices in commercial-grade systems where improved speed-power trade-offs and enhanced noise immunity were required.

FAQ

What logic family does SN74ALS157AD belong to, and how does it differ from standard 74LS?

SN74ALS157AD belongs to the Advanced Low-Power Schottky (ALS) logic family. It improves upon 74LS with ~30% lower ICC (6–11 mA vs. 19 mA typical for 74LS157), faster propagation delays (9 ns vs. 15 ns), and tighter VIH/VIL specs (2.0 V/0.8 V vs. 2.0 V/0.8 V, but with better noise margin). SN74ALS157AD retains full pin and function compatibility with 74LS157, enabling direct replacement in existing designs without layout changes.

Does SN74ALS157AD support 3-state outputs, and what happens when the strobe (G) input is high?

No, SN74ALS157AD does not have 3-state outputs. When the strobe (G) input is high (logic 1), all four outputs (1Y–4Y) are forced low regardless of A/B or data inputs. When G is low (logic 0), outputs reflect the selected input (A or B) as true-level signals. This active-low enable differs from 3-state operation - there is no high-impedance mode.

What is the maximum clock/data rate supported by SN74ALS157AD in a synchronous application?

SN74ALS157AD does not operate on a clock; it is a purely combinational device. Its usable data rate is governed by propagation delay and system timing margins. With worst-case tPHL/tPLH of 14 ns (G→Y) and 17 ns (A/B→Y) over temperature, it supports reliable operation in systems with ≥20 ns minimum cycle time - suitable for 50 MHz bus handshaking or slower synchronous control paths.

Can SN74ALS157AD be used with 3.3 V logic systems?

No, SN74ALS157AD is not 3.3 V compatible. It requires VCC = 4.5 V to 5.5 V and has TTL input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V). Driving its inputs from 3.3 V logic may result in marginal or failed high-level recognition. For 3.3 V systems, consider modern alternatives like SN74LVC157A, which supports 3.3 V operation and 5 V tolerant inputs.

Is SN74ALS157AD RoHS compliant, and what is its moisture sensitivity level?

Yes, SN74ALS157AD (specifically the SN74ALS157ADR and SN74ALS157ADR.A variants) is RoHS compliant with NiPdAu lead finish. Its moisture sensitivity level is rated MSL Level-1 (unlimited floor life), meaning it can be stored indefinitely at ≤30°C/60% RH and subjected to standard reflow profiles up to 260°C peak without baking.