Texas Instruments SN74HC623N

Overview

SN74HC623N 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, typical propagation delay of 8 ns, and operates across 2 V to 6 V supply voltage - enabling use in mixed-voltage industrial control backplanes and legacy TTL-to-CMOS interface applications.

For engineers reviewing the SN74HC623N datasheet, SN74HC623N pinout, SN74HC623N application, or SN74HC623N equivalent, key selection considerations include bidirectional bus isolation timing, lock-bus-latch capability under simultaneous OEAB/OEBA assertion, high-current 3-state output compatibility with LSTTL loads, and PDIP-20 package suitability for prototyping and through-hole production environments.

Technical Context

The SN74HC623N implements a true CMOS octal transceiver architecture with independent A→B and B→A data paths controlled by complementary OEAB (output-enable A-to-B) and OEBA (output-enable B-to-A) inputs. Its dual-enable logic allows simultaneous assertion to achieve bus-latch behavior, where both A and B buses retain their last valid states when all external drivers are tri-stated.

Each of the eight A-side and eight B-side I/Os supports 3-state operation with rail-to-rail output swing, ±6-mA drive strength at 5 V, and input leakage ≤1 µA. Propagation delay (tpd) is specified down to 8 ns at VCC = 6 V with CL = 50 pF, and enable/disable times (ten/tdis) range from 16 ns to 54 ns depending on supply and load conditions.

Key Specifications

Pinout & Package

SN74HC623N is housed in a 20-pin plastic dual in-line package (PDIP-N), 0.300-inch body width, with standard through-hole mounting and 0.100-inch lead pitch. Pin 1 is marked by a notch or dot at the top-left corner of the package.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT623N and 74LCX623M, the SN74HC623N uniquely balances wide 2–6 V operation, PDIP-20 availability for manual assembly, and lock-bus-latch functionality - making it the preferred choice for industrial upgrades, educational labs, and mixed-voltage bus bridging where layout flexibility and voltage adaptability are prioritized over minimum package size or TTL-level compatibility.

Availability

SN74HC623N is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus extensions, and programmable logic debug interfaces requiring stable component supply, long-term obsolescence management, and through-hole manufacturability.

Supply support for SN74HC623N 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 industry-standard logic families.

The SN74HC623N belongs to TI's 74HC high-speed CMOS logic product line, engineered for low-power, wide-voltage-range bidirectional data routing in industrial control, test equipment, and system-level interconnect applications.

FAQ

What is the maximum clock frequency supported by SN74HC623N in a synchronous bus application?

The SN74HC623N does not contain internal clocks or timing circuitry - it is an asynchronous transceiver. Its usable data rate depends on propagation delay (tpd = 8 ns typical at 6 V) and system-level setup/hold timing. For reliable operation with 50-pF loads, maximum toggle frequency is approximately 62.5 MHz assuming single-cycle data transfer; actual bus throughput must account for enable timing and external controller margins. The SN74HC623N itself imposes no hard clock limit.

Can SN74HC623N be used to replace SN74LS623 in existing 5-V designs?

Yes, SN74HC623N is a functional and pin-compatible replacement for SN74LS623 in 5-V systems, offering identical pinout, logic behavior, and 3-state control. Key improvements include lower ICC (80 µA vs. ~25 mA), higher noise immunity, and rail-to-rail output swing. However, note that SN74HC623N input thresholds differ: VIH = 3.15 V min at 4.5 V (vs. LS's 2 V), so verify upstream driver compatibility before substitution.

Does SN74HC623N support hot insertion or live bus swapping?

SN74HC623N is not rated for hot insertion. Its absolute maximum ratings specify no protection against supply sequencing or I/O voltage overshoot during live connection. While its 3-state outputs provide isolation, uncontrolled power-up sequencing or floating VCC/GND can cause latch-up or excessive current. For hot-swap applications, use dedicated hot-swap controllers or buffer ICs with built-in protection - the SN74HC623N should only be powered and enabled after stable supply and bus bias are established.

How does the lock-bus-latch feature of SN74HC623N work in practice?

When both OEAB and OEBA are driven low simultaneously, the SN74HC623N enters lock-bus-latch mode: each output reinforces its corresponding input, creating positive feedback. If all other drivers on both A and B buses are in high-impedance state, the 16 bus lines retain their last logic states indefinitely - effectively acting as a transparent 16-bit latch. This eliminates need for external latches in applications like interrupt acknowledge hold or bus state capture during debug.

Is SN74HC623N RoHS compliant and lead-free?

Yes, SN74HC623N is RoHS compliant and features lead-free (Pb-free) terminations with NiPdAu or NIPDAU finish, as confirmed in TI's official packaging addendum. The PDIP package uses matte tin plating over copper leadframe, meeting JEDEC J-STD-609 Category 1 requirements. Full compliance documentation, including material declarations and test reports, is available via TI's Quality & Environmental page for SN74HC623N.