Texas Instruments SN74HC623NSR

Overview

SN74HC623NSR 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), operates from 2 V to 6 V, delivers ±6-mA output drive at 5 V, and achieves typical propagation delay of 8 ns. It enables bidirectional data flow in industrial control backplanes and legacy microprocessor bus interfaces.

For engineers reviewing the SN74HC623NSR datasheet, SN74HC623NSR pinout, SN74HC623NSR application, or SN74HC623NSR equivalent, this page provides verified functional specifications, SOP-20 package details, lock-bus-latch capability, true logic compatibility with HC-family timing, and real-world use cases in isolated bus arbitration and level-shifted data routing.

Technical Context

The SN74HC623NSR implements a dual-enable octal transceiver architecture with independent OEAB (B→A) and OEBA (A→B) controls, enabling flexible direction selection and simultaneous bus isolation. Its CMOS design ensures low input current (≤1 µA) and high noise immunity across the full 2–6 V supply range.

When both OEAB and OEBA are asserted low, the device enters lock-bus-latch mode: outputs reinforce inputs, maintaining prior bus states on all 16 lines (A1–A8 and B1–B8) while other drivers are tri-stated - a critical feature for glitch-free bus hold during arbitration pauses.

Key Specifications

Pinout & Package

SOP-20 (NS) package: 20-pin surface-mount small-outline package, 0.300-inch body width, 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 SN74HC623NSR, SN74HCT623NSR improves TTL input compatibility at 5 V but sacrifices supply flexibility, while 74LCX623MTCX reduces propagation delay and power but eliminates 5 V operation - making SN74HC623NSR the optimal choice for industrial 2–6 V mixed-voltage bus isolation.

Availability

SN74HC623NSR is available at Aetrix Electronics and suitable for industrial backplane interfaces, microcontroller bus expansion, legacy system bus arbitration, and level-shifted peripheral interfacing requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN74HC623NSR 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 over 90 years of innovation in industrial, automotive, and communications markets.

The SN74HC623NSR belongs to TI's 74HC high-speed CMOS logic family, engineered for robust, low-power bidirectional bus interfacing in noise-sensitive industrial control and instrumentation systems.

FAQ

What is the maximum operating frequency supported by the SN74HC623NSR?

The SN74HC623NSR does not specify a maximum clock frequency, as it is an asynchronous transceiver. Its timing is governed by propagation delay (tpd = 8 ns typical at 5 V) and enable/disable times (ten/tdis ≈ 20–45 ns). For reliable operation, the minimum pulse width on data or enable signals must exceed the worst-case tpd + tdis, supporting effective bus handshaking up to approximately 125 MHz in well-designed layouts with 50 pF loads.

Does the SN74HC623NSR support 5 V logic levels when powered at 3.3 V?

No. When powered at VCC = 3.3 V, the SN74HC623NSR outputs swing from 0 V to 3.3 V, and its input thresholds scale accordingly (VIH ≈ 2.3 V, VIL ≈ 1.0 V per datasheet). It is not 5 V tolerant - applying 5 V signals to A/B pins or enables while VCC = 3.3 V may damage the device. Use SN74HCT623NSR for 5 V input compatibility at 3.3 V supply.

How does the lock-bus-latch mode work on the SN74HC623NSR?

When both OEAB and OEBA are driven low simultaneously, the SN74HC623NSR enters lock-bus-latch mode: each output reinforces its corresponding input, holding the last valid logic state on all 16 bus lines (A1–A8 and B1–B8). This occurs only if all other drivers on both buses are in high-impedance state - enabling glitch-free bus retention during arbitration pauses without external latches or clocks.

Is the SN74HC623NSR pin-compatible with the SN74HC245?

No. The SN74HC623NSR (SOP-20) has dual independent enables (OEAB/OEBA) and separate A/B I/O banks, while the SN74HC245 (also SOP-20) uses a single direction control (DIR) and shared enable (OE). Their pinouts differ: SN74HC623NSR places OEAB at Pin 1 and OEBA at Pin 12; SN74HC245 places DIR at Pin 1 and OE at Pin 19. PCB layout and firmware control logic are not interchangeable.

What is the thermal resistance (θJA) of the SN74HC623NSR in its SOP-20 package?

The SN74HC623NSR in the SOP-20 (NS) package has a junction-to-ambient thermal resistance (θJA) of 60°C/W, as specified in the TI datasheet SCLS149C. This value assumes standard JEDEC 2-layer board conditions (1 inch² copper pad, 2 oz Cu). Actual thermal performance depends on PCB layout, airflow, and adjacent heat sources - derating is recommended above 70°C ambient for continuous 80 µA ICC operation.