Texas Instruments SN74ALS667NT3

Overview

SN74ALS667NT3 from Texas Instruments is an 8-bit D-type transparent latch with true/inverted output logic (inverted for SN74ALS667), 3-state outputs, read-back capability via OERB control, and preset/clear inputs. It operates at 4.5–5.5 V, supports 0°C to 70°C ambient, and delivers 24 mA sink current on Q outputs - used in bus-oriented data storage and bidirectional bus interfacing in legacy TTL-based industrial control systems.

For engineers reviewing the SN74ALS667NT3 datasheet, SN74ALS667NT3 pinout, SN74ALS667NT3 application, or SN74ALS667NT3 equivalent, key selection criteria include its inverted-output behavior, bus-structured 24-pin DIP (NT) package, dual OE control for 3-state output management, OERB-enabled read-back functionality, and compatibility with ALS logic family timing and drive strength.

Technical Context

This device implements a parallel 8-bit transparent latch architecture where data passes through to Q outputs while LE is high; Q outputs reflect inverted D-input states. The latch includes independent preset (PRE) and clear (CLR) asynchronous controls, each requiring ≥10 ns pulse width for reliable assertion.

OERB enables bidirectional bus coupling: when low, stored latch outputs feed back onto D inputs; when high, D inputs are isolated. Output-enable logic uses active-low OE1 and OE2 - either high disables all Q outputs into high-impedance state, supporting shared-bus arbitration without external gating.

Key Specifications

Pinout & Package

SN74ALS667NT3 is supplied in a 300-mil plastic dual in-line package (DIP), designated NT, with 24 leads and standard through-hole mounting. Pin spacing follows JEDEC MS-001, compatible with legacy PCB footprints and socketing systems.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-bit transparent latch with read-back applications.

Compared with SN74ALS666NT3, SN74ALS667NT3 provides inverted output polarity essential for negative-logic bus protocols; compared with SN74ALS667DW, it offers through-hole reliability and serviceability at the cost of larger footprint and manual assembly requirements.

Availability

SN74ALS667NT3 is available at Aetrix Electronics and suitable for industrial PLC backplane interfaces, legacy test equipment data capture, military avionics diagnostics, and telecom line card configuration storage requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74ALS667NT3 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 with broad industrial and aerospace heritage.

The SN74ALS667NT3 belongs to TI's legacy ALS logic family, designed specifically for high-reliability, bus-structured digital systems requiring read-back verification, 3-state bus driving, and TTL-compatible timing in commercial temperature environments.

FAQ

What logic polarity does SN74ALS667NT3 implement at its Q outputs?

SN74ALS667NT3 provides inverted Q outputs - each Q pin reflects the logical complement of its corresponding D input when LE is high and outputs are enabled. This distinguishes it from SN74ALS666NT3, which provides true outputs. The inversion is hardwired and cannot be configured via external controls; it is intrinsic to the SN74ALS667NT3 silicon design and documented in the logic diagrams and functional description of the SDAS227A datasheet.

How does the OERB pin enable read-back functionality in SN74ALS667NT3?

OERB (Output Enable Read-Back) is an active-low control that connects the internal latch outputs directly to the D input bus when asserted low. When OERB is high, the D inputs are electrically isolated from the latch outputs - preserving input data integrity. This allows SN74ALS667NT3 to verify written data by latching, then reading back the same value without external components, provided bus conflict is avoided via coordinated OE control.

What are the absolute maximum ratings for SN74ALS667NT3 supply voltage and operating temperature?

The absolute maximum supply voltage for SN74ALS667NT3 is 7 V, and the absolute maximum input voltage on any pin (except D inputs) is also 7 V. For D inputs and disabled 3-state outputs, the limit is 5.5 V. The device is characterized for operation from 0°C to 70°C ambient - exceeding this range may cause parametric shift or permanent damage, and is not supported per the SDAS227A datasheet's recommended operating conditions table.

Can SN74ALS667NT3 be used interchangeably with SN74ALS667DW in the same design?

No - SN74ALS667NT3 and SN74ALS667DW share identical logic function, timing, and DC specifications but differ in package: NT is a 300-mil 24-pin DIP for through-hole mounting, while DW is a SOIC-24 surface-mount package. They are not physically interchangeable due to incompatible footprints, thermal profiles, and assembly methods. Board redesign is required to substitute one for the other, though firmware and schematic logic remain identical.

What is the minimum pulse width required for reliable assertion of CLR or PRE on SN74ALS667NT3?

The minimum pulse width for both CLR and PRE inputs on SN74ALS667NT3 is 10 ns under recommended operating conditions (VCC = 4.5–5.5 V, TA = 0°C to 70°C). This value is specified in the "recommended operating conditions" table of the SDAS227A datasheet and ensures full propagation through the internal asynchronous reset/set circuitry. Shorter pulses may result in metastability or incomplete bit clearing/presetting.