Texas Instruments SN74ALS137ADR

Overview

SN74ALS137ADR from Texas Instruments is a 3-line-to-8-line decoder/demultiplexer with integrated 3-bit address latch and dual output enables (G1, G2). It operates at 4.5–5.5 V, delivers ±0.4 mA high-level and 4–8 mA low-level output drive, and supports glitch-free strobed address decoding in bus-oriented systems. Its primary circuit role is address selection and latched decode control in legacy TTL-based memory and I/O expansion.

For engineers reviewing the SN74ALS137ADR datasheet, SN74ALS137ADR pinout, SN74ALS137ADR application, or SN74ALS137ADR equivalent, key selection considerations include latch-enable timing (tsu = 10 ns, th = 5 ns), propagation delays (tPLH/tPHL ≤ 20 ns), output enable independence, and compatibility with 74ALS logic families in industrial control and retro-computing designs.

Technical Context

The SN74ALS137ADR implements positive-logic decoding with asynchronous latch capture: when LE transitions high, A/B/C inputs are stored; subsequent changes are ignored until LE returns low. Output enables G1 and G2 operate independently-G1 low or G2 high forces all outputs high regardless of select or latch state.

It uses bipolar ALS (Advanced Low-Power Schottky) technology, delivering TTL-compatible voltage thresholds (VIH = 2 V, VIL = 0.8 V), guaranteed VOL ≤ 0.4 V at IOL = 4 mA, and ICC ≤ 11 mA at VCC = 5.5 V. Propagation delay from address or enable inputs to Y outputs is specified up to 20 ns under CL = 50 pF, RL = 500 Ω conditions.

Key Specifications

Pinout & Package

SN74ALS137ADR is supplied in a 16-pin SOIC (D) package (3.9 mm body width, 1.27 mm pitch), RoHS-compliant with NiPdAu lead finish. Pinout matches industry-standard 74xx137 layout for drop-in replacement in existing PCBs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ALS137ADR, SN74ALS138N removes latching capability but retains identical decode logic and enable architecture, while SN74AS137N trades power efficiency for raw speed and drive strength - making SN74ALS137ADR the optimal balance for legacy-compatible, thermally constrained, and glitch-sensitive applications.

Availability

SN74ALS137ADR is available at Aetrix Electronics and suitable for memory address decoding, I/O port selection, bus-oriented peripheral interface, and legacy system expansion requiring stable component supply and long-term obsolescence support.

Supply support for SN74ALS137ADR 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 for industrial, automotive, and communications markets.

The SN74ALS137ADR belongs to TI's legacy 74ALS logic family, designed specifically for low-power, high-reliability TTL-compatible digital systems in industrial control, test equipment, and retro-computing applications.

FAQ

What is the primary function of the SN74ALS137ADR in a digital system?

The SN74ALS137ADR functions as a 3-line-to-8-line decoder with integrated 3-bit address latch and dual output enables. It captures and holds a 3-bit address on the rising edge of LE, then decodes it to assert exactly one of eight active-low outputs (Y0–Y7) when both G1 is high and G2 is low. This makes SN74ALS137ADR ideal for glitch-free memory or I/O chip-select generation in bus-oriented systems where address stability during strobes is critical.

Does the SN74ALS137ADR require external components to operate as a decoder?

No, the SN74ALS137ADR operates as a complete decoder/latch without external components beyond standard 0.1 µF VCC decoupling. Its internal latch eliminates the need for an external 74ALS373 or similar device, and the dual output enables (G1, G2) allow direct hierarchical cascading. All timing parameters-including tsu = 10 ns and th = 5 ns-are met with standard TTL-level inputs, so no external timing resistors or capacitors are needed for basic operation of SN74ALS137ADR.

Can the SN74ALS137ADR replace a 74LS137 in an existing design?

Yes, the SN74ALS137ADR is pin-compatible and functionally equivalent to the 74LS137, with identical pinout, logic behavior, and DC/AC specifications. It offers improved power efficiency (lower ICC) and slightly faster propagation delays while maintaining full TTL voltage compatibility. Because SN74ALS137ADR meets or exceeds all 74LS137 timing and drive parameters, it can be used as a direct drop-in replacement in legacy designs without PCB or firmware changes.

What are the absolute maximum ratings for the SN74ALS137ADR?

The absolute maximum ratings for SN74ALS137ADR are: supply voltage VCC = 7 V, input voltage VI = 7 V, operating free-air temperature = 0°C to 70°C, and storage temperature = −65°C to 150°C. Exceeding any of these values may cause permanent damage. These are stress ratings only; functional operation is guaranteed only within the recommended operating conditions: VCC = 4.5–5.5 V, TA = 0°C to 70°C, and input voltages within VIH ≥ 2 V and VIL ≤ 0.8 V.

How does the latch-enable (LE) input affect output behavior in the SN74ALS137ADR?

In the SN74ALS137ADR, the LE input controls address sampling: when LE is low, the device acts as a transparent decoder - outputs respond immediately to A/B/C changes. On the rising edge of LE, the current A/B/C values are latched and held, and further input changes are ignored until LE goes low again. This ensures stable Y outputs even if the address bus changes during enable assertion - a key feature that prevents glitches in strobed bus systems using SN74ALS137ADR.