Texas Instruments SN74HC623NS

Overview

SN74HC623NS from Texas Instruments is an octal bus transceiver IC designed for asynchronous two-way data communication between parallel buses in digital systems. It features dual 3-state enable controls (OEAB/OEBA), ±6-mA output drive at 5 V, 8 ns typical propagation delay, and operates across 2 V to 6 V supply voltage. It enables bidirectional data flow with lock-bus-latch capability in industrial control backplanes and legacy microprocessor bus interfaces.

For engineers reviewing the SN74HC623NS datasheet, SN74HC623NS pinout, SN74HC623NS application, or SN74HC623NS equivalent, key selection considerations include its dual-enable 3-state logic, 20-pin SOP-NS package thermal performance (θ_JA = 60°C/W), wide V_CC range, and isolation timing parameters (t_dis = 16–45 ns).

Technical Context

The SN74HC623NS implements a CMOS-based octal transceiver architecture with independent A→B and B→A data paths controlled by OEAB and OEBA inputs. Its true logic design ensures no inversion, and simultaneous assertion of both enables creates a bus-latch state where all 16 bus lines retain their last values without external hold circuitry.

It supports asynchronous operation with separate enable-controlled directionality: OEAB = L enables B→A transmission; OEBA = L enables A→B transmission; both high isolates both buses. Output drive strength (±6 mA @ 5 V) and low ICC (80 µA max) make it suitable for mixed-voltage TTL/CMOS interfacing with minimal power impact.

Key Specifications

Pinout & Package

SOP-NS package: 20-pin surface-mount small-outline plastic package, 7.6 mm × 13.0 mm body, 1.27 mm pitch, 2.65 mm max height, RoHS-compliant NiPdAu lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC623NS, SN74HC245NSR offers simpler control but no latch capability, while SN74LVC245APW delivers higher speed and lower voltage operation at the cost of 5 V compatibility and different package thermal profile - making SN74HC623NS uniquely suited for industrial 5 V bus bridging with hold-state reliability.

Availability

SN74HC623NS is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy microprocessor bus extensions, and programmable logic controller I/O modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN74HC623NS 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 decades of heritage in industrial-grade logic families.

The SN74HC623NS belongs to TI's 74HC high-speed CMOS logic family, engineered for robust, low-power bidirectional data transfer in industrial control, instrumentation, and legacy system upgrades.

FAQ

What is the maximum operating frequency supported by the SN74HC623NS?

The SN74HC623NS does not specify a maximum clock frequency, as it is an asynchronous transceiver. Its 8 ns typical propagation delay (t_pd) at 6 V enables reliable operation with bus toggle periods down to ~20 ns - supporting effective data rates up to 50 MHz in well-terminated, low-capacitance layouts. Actual usable frequency depends on board trace length, load capacitance, and enable timing margins.

Can the SN74HC623NS operate at 3.3 V supply voltage?

Yes, the SN74HC623NS is fully specified for operation from 2 V to 6 V, including 3.3 V. At V_CC = 3.3 V, it delivers ±4 mA output drive, maintains VIH/VIL thresholds scaled to 70%/30% of V_CC, and exhibits t_pd ≈ 12 ns (typical). This makes SN74HC623NS suitable for interfacing 3.3 V logic to 5 V peripherals without level shifters.

How does the lock-bus-latch function work in the SN74HC623NS?

When both OEAB and OEBA are driven low simultaneously, the SN74HC623NS enters lock-bus-latch mode: each output reinforces its corresponding input, and with all external drivers in high-impedance state, both A and B buses retain their last logic states indefinitely. This behavior is intrinsic to the SN74HC623NS internal feedback design and requires no external clock or latch signals.

Is the SN74HC623NS pin-compatible with the SN74HC245NSR?

No, the SN74HC623NS is not pin-compatible with the SN74HC245NSR. Although both use 20-pin SOP-NS packages, their pin functions differ: SN74HC623NS has dedicated OEAB/OEBA pins (pins 1 and 19) and separate A/B bus ports, whereas SN74HC245NSR uses a single OE (pin 1) and direction (DIR, pin 19) input. Direct substitution would require PCB layout changes.

What is the thermal resistance (θ_JA) of the SN74HC623NS package?

The SN74HC623NS in the SOP-NS package has a junction-to-ambient thermal resistance (θ_JA) of 60°C/W, as specified in TI's official packaging documentation. This value assumes standard JEDEC 2-layer board conditions and is critical for calculating maximum allowable power dissipation in thermally constrained industrial enclosures where the SN74HC623NS may operate continuously at 85°C ambient.