Texas Instruments SN74ALS243AN

Overview

SN74ALS243AN from Texas Instruments is a quadruple 2-bit bus transceiver IC designed for asynchronous two-way data communication between parallel buses in TTL-compatible systems. It features dual output-enable controls (OEAB and OEBA), pnp-input circuitry to reduce DC loading, operates at 4.5–5.5 V, supports 0°C to 70°C ambient, and delivers ±12 mA output drive with 4–11 ns propagation delay.

For engineers reviewing the SN74ALS243AN datasheet, SN74ALS243AN pinout, SN74ALS243AN application, or SN74ALS243AN equivalent, this device is selected for bidirectional bus isolation, latch-mode data retention, and legacy TTL system interconnect where low input current and predictable 3-state timing are critical.

Technical Context

The SN74ALS243AN implements a dual-control 3-state transceiver architecture with independent A→B and B→A paths. Its pnp-input stage reduces input current to ≤±0.1 mA, minimizing loading on upstream drivers. The device supports four distinct functional modes-A-to-B transfer, B-to-A transfer, full isolation, and simultaneous latch-determined solely by OEAB/OEBA logic levels.

Timing behavior is defined by separate enable/disable delays (tPZH/tPLZ: 7–20 ns) and propagation delays (tPLH/tPHL: 4–11 ns), all measured under 50 pF load and 500 Ω source termination. Output voltage thresholds meet ALS-family specs: VOH ≥2.4 V at IOH = −12 mA, VOL ≤0.4 V at IOL = 12 mA.

Key Specifications

Pinout & Package

SN74ALS243AN uses a 14-pin plastic dual-in-line package (PDIP-N), with 0.3-inch width and through-hole mounting. Pin 7 is GND, pin 14 is VCC, and all I/O pins are arranged symmetrically for A-side (A1–A4) and B-side (B1–B4) data lines.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ALS240AN and SN74ALS244AN, the SN74ALS243AN uniquely supports true bidirectional, contention-free bus communication with integrated latch capability - making it the only option among the three for applications requiring dynamic direction switching and state hold without added logic.

Availability

SN74ALS243AN is available at Aetrix Electronics and suitable for legacy computer backplane interconnect, industrial PLC I/O module bus isolation, and embedded system memory expansion interfaces requiring stable component supply and long-term obsolescence management.

Supply support for SN74ALS243AN 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 for industrial, automotive, and communications markets.

The SN74ALS243AN belongs to TI's Advanced Low-Power Schottky (ALS) logic family, engineered for high-speed, low-power TTL-compatible digital interfacing in legacy and retrofit systems where reliability and backward compatibility are essential.

FAQ

What is the function of the OEAB and OEBA pins on the SN74ALS243AN?

The OEAB (Output Enable A→B) and OEBA (Output Enable B→A) pins are active-low controls that independently manage data flow direction on the SN74ALS243AN. When OEAB is low and OEBA is high, data passes from A to B; when OEBA is low and OEAB is high, data flows from B to A; when both are high, all outputs enter high-impedance isolation; when both are low, the device enters latch mode, retaining current bus states. This dual-control scheme is central to the SN74ALS243AN's flexible bus management capability.

Does the SN74ALS243AN support 3.3 V operation?

No, the SN74ALS243AN does not support 3.3 V operation. Its recommended supply voltage range is strictly 4.5 V to 5.5 V, and absolute maximum VCC is 7 V. Operation below 4.5 V risks incorrect logic thresholds and increased propagation delay; the SN74ALS243AN is designed exclusively for 5 V TTL-compatible systems. For 3.3 V applications, consider modern alternatives like the SN74LVC245A, but note these are not pin-compatible replacements for the SN74ALS243AN.

Can the SN74ALS243AN be used to replace the SN74LS243N in an existing design?

Yes, the SN74ALS243AN is a direct functional and pin-compatible upgrade for the SN74LS243N. It offers identical pinout, same 14-pin PDIP package, and improved specifications: lower input current (±0.1 mA vs. ±0.4 mA), faster propagation (4–11 ns vs. 6–20 ns), and higher output drive (±12 mA vs. ±8 mA). No PCB changes are required, and the SN74ALS243AN maintains full backward compatibility while enhancing noise immunity and timing margin in the same footprint.

What is the purpose of the NC pins on the SN74ALS243AN?

The SN74ALS243AN has two NC (No Connection) pins - pins 13 and 14 - which have no internal connection to die circuitry and must remain unconnected in the PCB layout. These pins exist due to package standardization across the ALS24x family and do not serve electrical, thermal, or mechanical functions. Leaving them floating is safe; soldering or routing to ground/VCC may cause unintended coupling or violate TI's layout guidance for the SN74ALS243AN.

How does the latch mode work on the SN74ALS243AN?

Latch mode on the SN74ALS243AN is activated when both OEAB and OEBA are driven low simultaneously. In this state, each output reinforces its corresponding input, allowing both A and B buses to retain their current logic states even when all other drivers on those buses are in high-impedance. This self-holding behavior eliminates the need for external latches in applications like memory address hold or test pattern capture - a unique capability of the SN74ALS243AN not found in most octal buffers or single-direction transceivers.