Texas Instruments SN74ALS645ADW

Overview

SN74ALS645ADW from Texas Instruments is an octal bus transceiver with 3-state outputs in a 20-pin SOIC (DW) package, designed for asynchronous bidirectional data transfer between A and B buses. It operates from 0°C to 70°C, supports 5-V supply, delivers ±12 mA output drive, and features direction-control (DIR) and output-enable (OE) logic for bus isolation in industrial control backplanes.

For engineers reviewing the SN74ALS645ADW datasheet, SN74ALS645ADW pinout, SN74ALS645ADW application, or SN74ALS645ADW equivalent, this page provides verified functional identity, validated pin roles, confirmed timing specs (tPLH ≤10 ns), absolute maximum ratings, and two rigorously cross-checked alternative parts for legacy TTL bus interface designs.

Technical Context

This device implements true TTL-compatible logic with active-low 3-state control: OE enables/disables all outputs simultaneously, while DIR selects data flow direction (A→B when high, B→A when low). No internal latching or clocking is present - operation is purely combinatorial and level-sensitive.

It belongs to the ALS (Advanced Low-Power Schottky) family, offering lower power than standard LS while maintaining compatible voltage thresholds (VIH = 2 V, VIL = 0.8 V) and improved speed over 74LS. The SN74ALS645ADW variant is rated for 12 mA sink/source per output at VCC = 5 V, distinct from the -1 version (48 mA IOL) and AS-series derivatives.

Key Specifications

Pinout & Package

SOIC-20 (DW) package: 7.5 mm × 12.8 mm body, 1.27 mm lead pitch, 2.65 mm max height, gull-wing leads, pin 1 marked by beveled corner or notch.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal bus transceiver applications.

Compared with SN74ALS645ADW, SN74ALS645ADWR offers identical performance in optimized packaging for SMT lines, while SN74AS645N trades package compatibility for significantly faster switching and stronger drive - both require validation of bus loading and timing closure in the target system.

Availability

SN74ALS645ADW is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy computer bus extensions, and test equipment signal routing requiring stable component supply and long-term obsolescence management.

Supply support for SN74ALS645ADW 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 ICs with broad industrial, automotive, and consumer reach.

The SN74ALS645ADW belongs to TI's legacy 74ALS logic family, engineered specifically for robust, low-power bidirectional bus interfacing in commercial-grade control and instrumentation systems.

FAQ

What is the operating voltage range for SN74ALS645ADW?

The SN74ALS645ADW operates strictly within 4.5 V to 5.5 V. It is not 3.3-V compatible, and operation below 4.5 V risks undefined logic states or failure to meet timing specs. The device draws ICC ≤60 mA when all outputs are active low, requiring proper 5-V regulation and local 0.1-µF ceramic decoupling at VCC pin 20.

Does SN74ALS645ADW support hot-swapping or live bus insertion?

SN74ALS645ADW supports controlled bus isolation via its OE input: asserting OE high places all 16 I/O pins in high-impedance state, preventing contention during module insertion. However, it lacks built-in bus-hold or power-up/down protection, so external series resistors and sequencing controls are recommended for true hot-swap reliability in SN74ALS645ADW-based systems.

What is the maximum data rate supported by SN74ALS645ADW?

Based on tPLH/tPHL ≤10 ns (VCC = 5 V, CL = 50 pF), SN74ALS645ADW supports reliable burst-mode data transfer up to ~25 MHz in point-to-point configurations. For sustained 8-bit parallel transfers, system-level timing must account for worst-case skew, trace length, and load capacitance - actual usable rate is typically 10–15 MHz in real backplane implementations using SN74ALS645ADW.

Is SN74ALS645ADW pin-compatible with SN74ALS645ADWR?

Yes, SN74ALS645ADW and SN74ALS645ADWR share identical SOIC-20 (DW) package dimensions, pinout, and electrical specifications. The only differences are packaging format (tube vs. tape-and-reel) and surface finish (older finish vs. RoHS-compliant NiPdAu); SN74ALS645ADWR is the recommended production variant for new designs using SN74ALS645ADW functionality.

Can SN74ALS645ADW replace SN74LS645 in existing designs?

Yes, SN74ALS645ADW is a direct functional and pin-compatible upgrade for SN74LS645, offering lower power consumption (ICC ≤60 mA vs. ~80 mA), faster propagation (≤10 ns vs. ≤15 ns), and improved noise immunity. No PCB changes are needed, but verify that the 12-mA output drive meets load requirements - SN74ALS645ADW may require minor termination adjustments in high-fanout LS-bus environments.