Texas Instruments SN74HCT645DW

Overview

SN74HCT645DW from Texas Instruments is an octal bus transceiver IC designed for asynchronous two-way data communication between A and B buses in 5-V TTL-compatible digital systems. It features direction control (DIR), 3-state output enable (OE), ±6-mA drive strength at 5 V, 14-ns typical propagation delay, and operates across 4.5 V to 5.5 V. It is used in bidirectional data buffering for microcontroller peripheral interfaces.

For engineers reviewing the SN74HCT645DW datasheet, SN74HCT645DW pinout, SN74HCT645DW application, or SN74HCT645DW equivalent, key selection criteria include bidirectional bus isolation timing, 3-state output leakage (≤5 µA), TTL-input compatibility, and SOIC-20 thermal performance (θ_JA = 58°C/W).

Technical Context

The SN74HCT645DW implements dual 8-bit bidirectional bus transceivers with independent DIR and OE controls. Its logic supports true-level translation: DIR = L enables B→A transfer; DIR = H enables A→B transfer; OE = H forces high-impedance isolation on both buses.

It uses HCMOS technology with TTL-compatible inputs (V_IL ≤ 0.8 V, V_IH ≥ 2 V) and CMOS-level outputs. Electrical behavior is specified over −40°C to 85°C, with absolute maximum V_CC = 7 V and continuous output current rating of ±35 mA per pin.

Key Specifications

Pinout & Package

SN74HCT645DW is housed in a 20-pin SOIC (DW) package measuring 7.5 mm × 12.8 mm × 2.65 mm (max height), with 1.27-mm lead pitch and RoHS-compliant NiPdAu finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT645DW, SN74LVC645APW enables 3.3-V integration but sacrifices TTL compatibility and drive strength, while 74ACT645SC improves speed and drive at the cost of significantly higher static power and thermal load - making SN74HCT645DW optimal for balanced 5-V industrial bus buffering.

Availability

SN74HCT645DW is available at Aetrix Electronics and suitable for microcontroller peripheral expansion, industrial backplane interfacing, legacy system bus bridging, and test equipment signal routing requiring stable component supply and long-term industrial lifecycle support.

Supply support for SN74HCT645DW 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 SN74HCT645DW belongs to TI's 74HCT high-speed CMOS logic series, engineered for seamless interoperability with TTL systems while delivering CMOS power efficiency and noise immunity in industrial control and instrumentation.

FAQ

What is the maximum operating temperature for the SN74HCT645DW?

The SN74HCT645DW is rated for operation from −40°C to +85°C ambient temperature. This industrial-grade specification ensures reliable performance in programmable logic controllers, motor drives, and factory automation equipment where enclosure temperatures may exceed consumer-grade limits. The SOIC-20 package's θ_JA of 58°C/W further supports thermal stability under continuous 5-V operation.

Does the SN74HCT645DW require external pull-up resistors on DIR or OE pins?

No, the SN74HCT645DW does not require external pull-up resistors on DIR or OE. Its inputs are TTL-compatible with defined V_IH ≥ 2.0 V and V_IL ≤ 0.8 V at V_CC = 4.5–5.5 V, and input current is limited to ±1 µA max. However, TI recommends tying unused inputs directly to V_CC or GND - not left floating - to prevent metastability or increased ICC, per Application Report SCBA004.

Can the SN74HCT645DW drive a 150-pF bus load while meeting timing specs?

Yes, the SN74HCT645DW maintains guaranteed timing with CL = 150 pF: t_pd ≤ 34 ns at V_CC = 5.5 V, t_en ≤ 67 ns, and t_dis ≤ 45 ns. These values are explicitly characterized in the datasheet's "Switching Characteristics" tables and validated across the full −40°C to +85°C range, making it suitable for backplane or ribbon-cable interconnects with significant distributed capacitance.

Is the SN74HCT645DW pin-compatible with other 74HCT645 variants like SN74HCT645N or SN74HCT645PW?

Yes, all 74HCT645 variants - including SN74HCT645N (PDIP), SN74HCT645PW (TSSOP), and SN74HCT645DW (SOIC) - share identical pinouts and electrical functionality. The 20-pin arrangement, signal assignments (DIR, OE, A1–A8, B1–B8, V_CC, GND), and logic behavior are standardized across packages. Only mechanical dimensions, thermal resistance, and packaging differ - enabling direct PCB footprint substitution where board space and reflow profile allow.

What is the 3-state output leakage current specification for the SN74HCT645DW?

The SN74HCT645DW specifies a maximum 3-state output leakage current (I_OZ) of ±5 µA at V_CC = 5.5 V and T_A = 25°C, with ±10 µA guaranteed over the full operating temperature range. This low leakage ensures minimal bus loading during isolation, preserving signal integrity and preventing unintended activation of downstream receivers when OE = high.