Texas Instruments SN74AS131AD

Overview

SN74AS131AD from Texas Instruments is a 3-line-to-8-line decoder/demultiplexer with integrated address registers and dual enable inputs. It operates at 5 V, supports up to 100 MHz clock frequency, features 20 mA low-level output drive, and is designed for glitch-free strobed address decoding in bus-oriented systems.

For engineers reviewing the SN74AS131AD datasheet, SN74AS131AD pinout, SN74AS131AD application, or SN74AS131AD equivalent, key selection criteria include registered address latching on CLK rising edge, independent G1/G2 output-enable control, 9.5–14.5 ns propagation delays, and compatibility with 5-V TTL/AS logic families.

Technical Context

The SN74AS131AD implements synchronous address capture using positive-edge-triggered D-type flip-flops on A, B, and C inputs, ensuring stable output selection during address transitions. Its dual enable architecture (G1 high + G2 low) allows hierarchical cascading without external gating logic.

Outputs are active-low decoded signals (Y0–Y7), each capable of sinking 20 mA while maintaining VOL ≤ 0.5 V at VCC = 4.5 V. Propagation delay from CLK to Y is 2–14.5 ns, and from G1/G2 to Y is 7–10 ns, enabling precise timing control in high-speed bus arbitration.

Key Specifications

Pinout & Package

SN74AS131AD is housed in a 16-pin SOIC (D package), 3.9 mm wide, with standard 1.27 mm pitch. Pin numbering follows JEDEC MS-012, top-view orientation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ALS138N and SN74F138N, the SN74AS131AD uniquely combines 100-MHz clocked registration with 20-mA drive and dual-enable flexibility-making it the only option among the three for reliable strobed decoding in electrically noisy or dynamically addressed bus systems.

Availability

SN74AS131AD is available at Aetrix Electronics and suitable for memory address decoding, bus arbitration logic, I/O port expansion, programmable logic interface, and industrial control subsystems requiring stable component supply and long-term design continuity.

Supply support for SN74AS131AD 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 company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74AS131AD belongs to TI's advanced Schottky (AS) logic family, engineered for high-speed, low-glitch performance in bus-oriented digital systems requiring registered address decoding.

FAQ

What is the primary function of the SN74AS131AD?

The SN74AS131AD is a 3-line-to-8-line decoder/demultiplexer with integrated D-type registers on its A, B, and C address inputs. It captures and holds the address on the rising edge of CLK, then decodes it to assert exactly one of eight active-low outputs (Y0–Y7), provided G1 is high and G2 is low. This registered behavior prevents output glitches during address transitions, distinguishing it from combinational-only decoders like the SN74AS138.

Does the SN74AS131AD support 3.3-V operation?

No, the SN74AS131AD is specified only for 4.5 V to 5.5 V supply operation and is not rated for 3.3-V use. Its input thresholds (VIH = 2.0 V, VIL = 0.8 V) and output drive characteristics are optimized for 5-V TTL/AS logic families. Attempting 3.3-V operation may result in unreliable switching, excessive ICC, or failure to meet timing specifications. For 3.3-V systems, consider modern alternatives such as the SN74LVC138A.

How does the enable logic work on the SN74AS131AD?

The SN74AS131AD uses two independent enable inputs: G1 (active-high) and G2 (active-low). All outputs go high-impedance (inactive) unless G1 = high AND G2 = low. This ANDed enable condition allows hierarchical cascading-e.g., one SN74AS131AD can enable the G2 input of another using its Y output-without external logic gates. Unlike single-enable decoders, this dual-input scheme simplifies multi-level decode trees in large address spaces.

What is the maximum clock frequency supported by the SN74AS131AD?

The SN74AS131AD supports a maximum clock frequency of 100 MHz under recommended operating conditions (VCC = 4.5 V to 5.5 V, CL = 50 pF, TA = 0°C to 70°C). This rating is validated by the fmax parameter in the switching characteristics table and reflects the device's ability to reliably capture and decode addresses at sub-10-ns intervals. Sustained operation above 100 MHz risks setup/hold violations or metastability in the internal registers.

Is the SN74AS131AD still in production?

No, the SN74AS131AD is marked as OBSOLETE by Texas Instruments per its official packaging information. While Aetrix Electronics maintains legacy inventory and offers traceable, tested units for design continuity and repair, new designs should evaluate functionally equivalent modern replacements. TI does not manufacture or warrant new shipments of SN74AS131AD, and long-term supply depends on remaining stock and redistribution channels.