Texas Instruments SN74ALS623ANS

Overview

SN74ALS623ANS from Texas Instruments is an octal bus transceiver with 3-state outputs and active-low output-enable control, fabricated using advanced bipolar ALS (Advanced Low-Power Schottky) technology. It operates at VCC = 5 V, supports ±24 mA output drive, features typical propagation delay of 11 ns (A→B), and is housed in a 20-pin plastic small-outline (SO) package. It enables bidirectional data flow between two 8-bit buses in microprocessor system data paths.

For engineers reviewing the SN74ALS623ANS datasheet, SN74ALS623ANS pinout, SN74ALS623ANS application, or SN74ALS623ANS equivalent, key selection considerations include its 3-state bus-hold capability, ALS logic family speed-power trade-off, 5-V-only operation, and compatibility with LS/TTL input thresholds in mixed-logic systems.

Technical Context

The SN74ALS623ANS implements dual 4-bit directional control logic: one set of four bits transfers from A to B when OE̅ is low and DIR is high; the other four transfer from B to A when OE̅ is low and DIR is low. Its ALS process delivers lower power than standard LS while maintaining comparable speed.

All inputs are TTL-compatible with VIH = 2.0 V min and VIL = 0.8 V max; outputs drive standard TTL loads with VOH = 2.7 V min at IOH = –0.4 mA and VOL = 0.5 V max at IOL = 24 mA. The device lacks internal bus-hold or weak pull-up circuitry - external termination is required for floating-bus stability.

Key Specifications

Pinout & Package

SN74ALS623ANS is supplied in a 20-pin plastic small-outline (SO) package per TI drawing NS, with 0.300-inch body width and gull-wing leads. Pin 1 is located at the top-left corner (Q1 quadrant), with pin numbering counterclockwise.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS623NSR and SN74F623N, the SN74ALS623ANS offers the optimal balance of speed (11 ns), power (19 mW), and SO-package compatibility for space-constrained 5-V digital systems requiring reliable bidirectional bus control.

Availability

SN74ALS623ANS is available at Aetrix Electronics and suitable for microprocessor bus interfaces, industrial backplane interconnects, and legacy test equipment signal routing requiring stable component supply and long-term obsolescence management.

Supply support for SN74ALS623ANS 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 headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and consumer markets since 1930.

The SN74ALS623ANS belongs to TI's legacy TTL logic portfolio, designed specifically for 5-V digital system interconnect in microprocessor-based equipment, instrumentation, and industrial controllers where ALS speed-power characteristics were critical.

FAQ

What logic family does the SN74ALS623ANS belong to, and how does it differ from standard LS?

The SN74ALS623ANS belongs to the Advanced Low-Power Schottky (ALS) logic family. Compared to standard LS, it achieves approximately 40% lower power consumption (19 mW vs. ~35 mW per channel) while maintaining comparable speed - 11 ns typical propagation delay versus 15 ns for SN74LS623NSR. Both share identical pinout and TTL-compatible input thresholds, making SN74ALS623ANS a drop-in power-optimized upgrade in existing LS-based designs where thermal or supply constraints exist.

Does the SN74ALS623ANS support mixed-voltage operation or 3.3-V interface?

No, the SN74ALS623ANS is strictly a 5-V-only device with VCC = 5 V ±5%. It does not support 3.3-V operation, nor does it feature 5-V tolerant inputs for use with lower-voltage logic. Its input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) are compatible with 3.3-V CMOS outputs only if those outputs guarantee VOH ≥ 2.4 V and VOL ≤ 0.4 V - which many do not. Direct interfacing with 3.3-V systems requires level-shifting circuitry or a dedicated voltage-tolerant transceiver such as the SN74LVC8T245.

What is the function of the DIR and OE̅ pins on the SN74ALS623ANS?

The DIR (direction) pin controls data flow direction: when DIR = high, data passes from port A to port B; when DIR = low, data flows from port B to port A. The OE̅ (output enable, active-low) pin enables or disables all outputs: when OE̅ = low, outputs are active and bidirectional data transfer occurs; when OE̅ = high, all outputs enter high-impedance state regardless of DIR state. These two control signals allow precise bus arbitration and isolation in multi-master systems - a core functionality implemented in the SN74ALS623ANS design.

Is the SN74ALS623ANS pin-compatible with the SN74LS623NSR?

Yes, the SN74ALS623ANS is fully pin-compatible with the SN74LS623NSR: both use the same 20-pin SO (NS) package, identical pinout, and identical terminal functions. This allows direct PCB-level substitution without layout changes. However, timing and power differences must be verified - SN74ALS623ANS offers faster propagation (11 ns vs. 15 ns) and lower power (19 mW vs. 35 mW), which may affect system timing closure or thermal design in high-density layouts.

What are the recommended decoupling practices for the SN74ALS623ANS?

Each SN74ALS623ANS requires a minimum 0.1-μF ceramic capacitor placed as close as possible to the VCC (pin 20) and GND (pin 11) pins, with short, low-inductance traces. For boards with multiple SN74ALS623ANS devices, add a bulk 4.7-μF tantalum or aluminum electrolytic capacitor near the power entry point. Avoid shared vias between decoupling caps and IC pins; use separate ground vias for each device to minimize ground bounce. These practices ensure stable 5-V supply delivery and suppress switching noise generated by the ±24 mA output transitions in the SN74ALS623ANS.