Texas Instruments SN74AS646NTG4

Overview

SN74AS646NTG4 from Texas Instruments is an octal bus transceiver and register IC with 3-state outputs, independent A/B bus registers, true (non-inverting) data path, and real-time/stored data multiplexing capability. It operates at up to 90 MHz clock frequency, supports 5 V supply, and delivers 48 mA low-level output drive - enabling high-speed bidirectional data routing in legacy TTL-compatible systems such as industrial backplanes and test equipment.

For engineers reviewing the SN74AS646NTG4 datasheet, SN74AS646NTG4 pinout, SN74AS646NTG4 application, or SN74AS646NTG4 equivalent, key selection criteria include its 24-pin PDIP (NT) package, DIR/CLKAB/CLKBA-controlled bus direction and storage timing, OE-gated 3-state outputs, and compatibility with SN74AS648 (inverting variant) in shared bus architectures.

Technical Context

The SN74AS646NTG4 integrates dual 8-bit D-type flip-flop registers (A and B buses), asynchronous select logic (SAB/SBA), and a direction-controlled transceiver core. Its clock inputs (CLKAB, CLKBA) latch data on low-to-high transitions, while DIR determines active bus direction during OE-enabled transfer.

It implements glitch-free multiplexing between real-time (transparent) and stored data paths via dedicated SAB/SBA control, eliminating decoding hazards during mode switching. The device maintains full input enablement even when outputs are disabled (OE high), supporting concurrent data capture and storage across both buses.

Key Specifications

Pinout & Package

SN74AS646NTG4 uses a 24-pin plastic DIP (NT) package with 300-mil width, through-hole mounting, and industry-standard pin spacing. Pin 1 is top-left corner (notch side), with pins numbered counter-clockwise.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74AS648DW, SN74AS646NTG4 provides non-inverting transparency essential for diagnostic visibility; versus SN74ALS646ADW, it delivers 2.25× higher clock rate and double the output current - critical for noise-immune, high-density bus interfaces.

Availability

SN74AS646NTG4 is available at Aetrix Electronics and suitable for industrial backplane interfaces, automated test equipment bus controllers, and legacy system bus arbitration requiring stable component supply and long-term obsolescence management.

Supply support for SN74AS646NTG4 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 specializing in analog, embedded processing, and logic solutions with over 50 years of innovation in industrial, automotive, and communications markets.

The SN74AS646NTG4 belongs to TI's Advanced Schottky TTL logic family, designed specifically for high-speed, noise-tolerant bus interfacing in mission-critical industrial and test instrumentation systems.

FAQ

What is the maximum clock frequency supported by SN74AS646NTG4?

The SN74AS646NTG4 supports a maximum clock frequency of 90 MHz under recommended operating conditions (VCC = 4.5 V to 5.5 V, TA = 0°C to 70°C). This rating applies to both CLKAB and CLKBA inputs and is validated per TI's characterization data for SN74AS646 devices. The SN74AS646NTG4 achieves this performance using Advanced Schottky TTL circuitry optimized for minimal propagation delay and fast edge response.

Does SN74AS646NTG4 support true or inverting data transfer?

SN74AS646NTG4 implements a true (non-inverting) data path. When configured for real-time transfer (e.g., DIR = H, SAB = L), data appearing at A1–A8 passes directly to B1–B8 without polarity inversion. This behavior is confirmed in the function tables and logic diagrams of the SDAS039F datasheet, distinguishing it from the inverting SN74AS648 variant. The SN74AS646NTG4's true-path design preserves signal integrity for debugging, monitoring, and deterministic bus protocols.

What package type is used for SN74AS646NTG4?

SN74AS646NTG4 uses a 24-pin plastic dual in-line package (PDIP) with NT suffix, featuring 300-mil body width and through-hole mounting. This package is explicitly listed in TI's packaging addendum and matches the pinout diagram labeled "NT PACKAGE" in the SDAS039F datasheet. The NT package provides mechanical robustness and thermal performance suited for industrial PCBs where reflow compatibility is not required.

Can SN74AS646NTG4 operate with 3.3 V logic levels?

No, SN74AS646NTG4 is specified exclusively for 5 V operation (VCC = 4.5 V to 5.5 V) and is not 3.3 V tolerant. Its input thresholds (VIH = 2 V, VIL = 0.8 V) and output voltage levels (VOH ≥ 2.4 V, VOL ≤ 0.5 V at 48 mA) are designed for TTL/LS compatibility. Driving SN74AS646NTG4 inputs from 3.3 V logic may result in marginal noise margins or failure to meet VIH/VIL specifications. Level-shifting circuitry is required for interoperability with 3.3 V systems.

How does SN74AS646NTG4 handle bus isolation during OE high?

When OE is high, all A1–A8 and B1–B8 outputs enter high-impedance (3-state) mode, electrically isolating both buses. Critically, input functionality remains fully enabled: data present on either bus continues to be sampled and latched into the respective A or B register on every low-to-high CLKAB or CLKBA transition. This allows SN74AS646NTG4 to maintain real-time data capture capability even while physically disconnecting buses - a key feature for fault containment and hot-swap readiness.