Texas Instruments SN74HC645DWR

Overview

SN74HC645DWR from Texas Instruments is an octal bus transceiver IC designed for asynchronous bidirectional data transfer between two 8-bit buses. It operates across 2 V to 6 V, delivers ±6-mA output drive at 5 V, exhibits typical propagation delay of 12 ns, and features high-current 3-state outputs capable of driving up to 15 LSTTL loads - used in microcontroller peripheral interfacing and legacy bus isolation.

For engineers reviewing the SN74HC645DWR datasheet, SN74HC645DWR pinout, SN74HC645DWR application, or SN74HC645DWR equivalent, key selection considerations include direction-control (DIR) and output-enable (OE) logic behavior, SOIC-20 package thermal performance (θ_JA = 58°C/W), and compatibility with HC-family voltage thresholds and timing budgets in mixed-voltage digital systems.

Technical Context

This device implements dual 8-bit bidirectional data paths controlled by DIR (direction) and OE (output enable) inputs. When OE is low, data flows either A→B (DIR = high) or B→A (DIR = low); when OE is high, all outputs enter high-impedance state, isolating both buses. The logic is true (non-inverting) and fully compatible with standard CMOS input thresholds.

It uses silicon-gate CMOS technology for low power consumption (ICC ≤ 80 µA max) and robust noise immunity. Input transition times are specified down to 400 ns (at VCC = 6 V), and output transition times (tt) range from 6 ns to 15 ns depending on supply voltage and load - enabling reliable operation in 20-MHz-class synchronous and asynchronous bus environments.

Key Specifications

Pinout & Package

SN74HC645DWR is housed in a 20-pin SOIC (DW) package, 7.5 mm wide, 12.8 mm long, 2.65 mm max height, with 1.27 mm pitch and RoHS-compliant NiPdAu lead finish. Moisture sensitivity level is Level-1 (unlimited floor life at ≤30°C/60% RH).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC645DWR, SN74HCT645DWR offers improved noise immunity in noisy 5 V environments but consumes slightly more quiescent current; 74LVC245APW,118 delivers superior speed and lower voltage operation but mandates redesign due to non-identical pin mapping and package footprint.

Availability

SN74HC645DWR is available at Aetrix Electronics and suitable for industrial control interfaces, test equipment signal routing, and microcontroller peripheral expansion requiring stable component supply and long-term manufacturing continuity.

Supply support for SN74HC645DWR 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 company headquartered in Dallas, Texas, delivering analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74HC645DWR belongs to TI's 74HC logic family - engineered for high noise immunity, low power, and broad voltage operation in general-purpose digital interface and bus management applications.

FAQ

What is the maximum operating temperature range for SN74HC645DWR?

The SN74HC645DWR is rated for operation from –40°C to +85°C ambient temperature. This industrial-grade range is validated per TI's recommended operating conditions and supported by thermal characterization (θ_JA = 58°C/W for the DW package). Derating is required above 70°C ambient if power dissipation exceeds 150 mW; full functionality is guaranteed across the entire range when proper PCB thermal design is applied.

Does SN74HC645DWR support 3.3 V operation with guaranteed timing performance?

Yes, SN74HC645DWR supports 3.3 V operation with fully characterized timing: typical propagation delay is 15 ns (max 32 ns) at VCC = 3.3 V, CL = 50 pF, TA = 25°C. Input thresholds (VIH = 2.0 V min, VIL = 0.99 V max) and output drive (±4 mA min) are specified across the full 2–6 V range, ensuring reliable interface with 3.3 V microcontrollers and FPGAs without level translation.

Can SN74HC645DWR be used as a unidirectional buffer by fixing the DIR pin?

Yes, SN74HC645DWR can operate unidirectionally by tying DIR permanently high (A→B only) or low (B→A only). In this mode, it functions as an 8-bit non-inverting buffer with 3-state control via OE. No timing or drive degradation occurs; all specifications - including tpd, output current, and ICC - remain identical to bidirectional use, provided OE and DIR are driven by clean, low-noise logic sources.

What is the recommended PCB layout practice for SN74HC645DWR to minimize ground bounce?

Place a 0.1 µF ceramic decoupling capacitor between VCC (pin 20) and GND (pin 10) with trace length <5 mm. Use a solid ground plane beneath the SOIC-20 footprint, route GND and VCC traces wide (>0.3 mm), and avoid splitting the ground plane under the device. TI's DW package land pattern (MS-013 compliant) specifies 1.27 mm pitch and 0.51 mm lead width - adherence to this ensures optimal thermal and electrical performance for SN74HC645DWR.

Is SN74HC645DWR pin-compatible with SN74LS645 or other TTL transceivers?

No, SN74HC645DWR is not pin-compatible with SN74LS645. While both are 20-pin octal transceivers, the LS version uses different pin assignments: DIR is on pin 11, OE on pin 1, and GND/VCC locations differ. Additionally, SN74HC645DWR has CMOS input thresholds and lower drive strength than LS logic. Direct replacement requires PCB redesign and logic-level validation - TI does not list SN74LS645 as a functional or pin-compatible alternative for SN74HC645DWR.