Texas Instruments SN74HCT623N

Overview

SN74HCT623N from Texas Instruments is an octal bus transceiver with 3-state outputs, designed for asynchronous bidirectional data transfer between A and B buses in TTL-compatible systems. It operates at 4.5 V to 5.5 V, delivers ±6-mA output drive, exhibits 11-ns typical propagation delay, and supports lock-bus latch functionality via dual OE control (OEAB/OEBA). It is used in industrial backplane interfaces requiring isolated bus communication.

For engineers reviewing the SN74HCT623N datasheet, SN74HCT623N pinout, SN74HCT623N application, or SN74HCT623N equivalent, key selection criteria include dual-directional 3-state control timing, TTL-input compatibility, 8-bit bus isolation capability, and PDIP-20 package suitability for through-hole prototyping and legacy board upgrades.

Technical Context

The SN74HCT623N implements a dual-output-enable architecture enabling independent or simultaneous A→B, B→A, or high-impedance isolation modes. Its logic diagram confirms true bidirectional signal reinforcement when both OEAB and OEBA are low, preserving bus states without external latching.

It meets HCT logic family specifications: input thresholds match TTL voltage levels (VIH = 2 V min, VIL = 0.8 V max), ICC remains ≤80 µA at VCC = 5.5 V, and output drive sustains ±6 mA while maintaining VOL ≤0.33 V and VOH ≥3.7 V under load - ensuring robust interfacing with LSTTL loads.

Key Specifications

Pinout & Package

SN74HCT623N is housed in a 20-pin plastic dual in-line package (PDIP-N), with 0.3-inch body width and through-hole mounting. Thermal resistance θJA is 69°C/W, suitable for natural-convection cooling in industrial control modules.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT245N and 74ACT245PC, the SN74HCT623N uniquely supports simultaneous bidirectional bus retention via dual OE, making it optimal for applications requiring transparent data hold without clocks or memory elements - a capability neither alternative provides.

Availability

SN74HCT623N is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy bus extensions, automated test equipment data routing, and programmable logic controller I/O modules requiring stable component supply and long-term obsolescence support.

Supply support for SN74HCT623N 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 ICs for industrial, automotive, and communications markets.

The SN74HCT623N belongs to TI's 74HCT logic family, engineered for TTL-compatible operation in 5-V systems where low power, noise immunity, and bus isolation are essential - particularly in legacy infrastructure and maintenance-critical equipment.

FAQ

What is the recommended power-up sequence for SN74HCT623N to ensure high-impedance outputs?

To guarantee high-impedance outputs during power-up, tie OEBA to VCC via a pullup resistor and OEAB to GND via a pulldown resistor. The minimum resistor value depends on the driver's current-sinking/sourcing capability - typically 10 kΩ suffices for most microcontroller GPIOs. This prevents bus contention before firmware initializes OE control lines in the SN74HCT623N.

Can SN74HCT623N interface directly with 3.3-V logic devices?

No, SN74HCT623N is not 3.3-V tolerant: its absolute maximum input voltage is 7 V, but VIH minimum is 2 V at VCC = 4.5–5.5 V - meaning 3.3-V logic HIGH may fall below guaranteed recognition threshold. Direct connection risks unreliable operation. Use level-shifting circuitry or a 3.3-V–compatible transceiver like SN74LVC245A when interfacing with 3.3-V systems alongside SN74HCT623N.

How does the lock-bus latch function work in SN74HCT623N?

When both OEAB and OEBA are driven low simultaneously, the SN74HCT623N enters lock-bus latch mode: each output reinforces its corresponding input, and if all other drivers on both A and B buses are in high-impedance state, the 16 bus lines retain their last logic states. This behavior is purely combinational - no clock or storage element is involved - and is intrinsic to the SN74HCT623N's internal architecture.

What is the maximum capacitive load SN74HCT623N can drive while maintaining specified timing?

The SN74HCT623N's switching characteristics are characterized at CL = 50 pF and CL = 150 pF. At 5.5 V supply, tpd increases from 13 ns (50 pF) to 34 ns (150 pF); setup/hold and enable/disable times also scale accordingly. For designs requiring <20 ns propagation, keep total load (including trace and input capacitance) below 75 pF. Exceeding 150 pF may violate timing margins in high-speed SN74HCT623N applications.

Is SN74HCT623N RoHS compliant and what is its moisture sensitivity level?

Yes, SN74HCT623N is RoHS compliant (lead-free NIPDAU finish). As a PDIP package, it carries no MSL rating - moisture sensitivity level is "N/A for Pkg Type" per TI's packaging documentation. No bake preconditioning is required prior to through-hole soldering, and the device may be stored indefinitely under standard dry ambient conditions without special handling.