Texas Instruments SN74ALS156N

Overview

SN74ALS156N from Texas Instruments is a dual 2-line-to-4-line decoder/demultiplexer IC in a 16-pin PDIP package, featuring independent strobes (1G, 2G), common binary address inputs (A, B), and complementary data paths (1C inverted, 2C non-inverted). It operates across 0°C to 70°C with VCC = 4.5–5.5 V, supports 3-line-to-8-line decoding via interconnect, and delivers tPHL as low as 6 ns for critical timing paths in legacy TTL-based control logic.

For engineers reviewing the SN74ALS156N datasheet, SN74ALS156N pinout, SN74ALS156N application, or SN74ALS156N equivalent, key selection criteria include its dual-section enable control, Schottky-clamped inputs for ringing suppression, guaranteed 8-mA sink capability, and compatibility with ALS-family logic levels in industrial control panels and retro-computing bus interfaces.

Technical Context

The SN74ALS156N implements two independent 2-to-4 decoder/demux sections sharing address lines A and B but with separate data inputs (1C, 2C) and strobes (1G, 2G). Its internal logic includes an inverter on the 1C path, enabling direct 3-to-8-line demux operation when 1C and 2C are tied together with shared strobe G.

Designed for bipolar ALS (Advanced Low-power Schottky) technology, it features Schottky-clamped inputs to suppress line ringing, supports open-collector-compatible outputs with VOL ≤ 0.5 V at IOL = 8 mA, and meets absolute maximum ratings up to 7 V on VCC and VI - ensuring robustness in noisy industrial backplanes.

Key Specifications

Pinout & Package

SN74ALS156N uses a 16-pin plastic DIP (PDIP) package with 300-mil width, standard through-hole footprint, and industry-compatible lead spacing (0.1" pitch).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar decoder/demultiplexer applications.

Compared with SN74LS156N, SN74ALS156N offers 29% faster switching and 53% lower power; versus SN74HC138N, it maintains TTL-compatible thresholds and push-pull outputs but lacks CMOS-level static power efficiency - making it optimal for upgrading aging LS-based systems without board changes.

Availability

SN74ALS156N is available at Aetrix Electronics and suitable for industrial PLC I/O expansion, retrocomputing address decoding, and legacy test equipment control logic requiring stable component supply and long-term obsolescence management.

Supply support for SN74ALS156N 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, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74ALS156N belongs to TI's Advanced Low-power Schottky (ALS) logic family, designed specifically to upgrade LS-TTL systems with improved speed, reduced power, and enhanced noise immunity - targeting backward-compatible replacements in mission-critical industrial control hardware.

FAQ

What logic family does the SN74ALS156N belong to, and how does it differ from standard LS-TTL?

The SN74ALS156N belongs to Texas Instruments' Advanced Low-power Schottky (ALS) logic family. It differs from standard LS-TTL by delivering faster propagation delays (e.g., 25 ns max tPHL vs. 35 ns for SN74LS156N) and lower power consumption (9 mA typical ICC vs. 19 mA), while retaining identical pinout, voltage thresholds, and functional behavior - enabling direct drop-in upgrades in existing LS-based designs without layout changes.

Can the SN74ALS156N be used as a 3-line-to-8-line decoder, and if so, how is it configured?

Yes, the SN74ALS156N can function as a 3-line-to-8-line decoder. To configure it, connect inputs 1C and 2C together as the third address bit (C), tie strobes 1G and 2G together as the common enable (G), and apply A and B to their respective pins. The inverter on the 1C path ensures complementary outputs across both sections, generating all eight decoded outputs (1Y0–1Y3 and 2Y0–2Y3) without external gates - a capability explicitly confirmed in the SN74ALS156N datasheet function tables.

What is the maximum output sink current supported by the SN74ALS156N, and under what conditions is it specified?

The SN74ALS156N supports a minimum output sink current (IOL) of 8 mA per output, specified at VCC = 4.5 V and VO = 0.5 V. This rating ensures reliable driving of multiple standard TTL inputs (each requiring ~1.6 mA) or small indicator LEDs without external buffers. The value is guaranteed across the full operating temperature range (0°C to 70°C) and aligns with ALS-family design margins for sustained current delivery in industrial control applications.

Does the SN74ALS156N include input protection, and what type is implemented?

Yes, the SN74ALS156N includes high-performance Schottky diode clamping on all inputs. These diodes suppress transmission-line ringing caused by fast edge rates and unterminated traces - a common issue in backplane and ribbon-cable interconnects. This feature simplifies system design by reducing or eliminating the need for external RC snubbers or series resistors, particularly in electrically noisy industrial environments where the SN74ALS156N is commonly deployed.

Is the SN74ALS156N RoHS compliant, and what is its packaging format?

Yes, the SN74ALS156N is RoHS compliant, with lead finish specified as NiPdAu (nickel-palladium-gold) per TI's packaging documentation. It is supplied in a 16-pin plastic dual in-line package (PDIP, "N" suffix) with 300-mil width, packaged in tubes of 25 units. The device carries a commercial temperature rating (0°C to 70°C) and is marked "SN74ALS156N" on the top surface - matching TI's official orderable part number and package option addendum.