Texas Instruments SN74HCT645PWR

Overview

SN74HCT645PWR from Texas Instruments is an octal bus transceiver IC designed for asynchronous two-way data communication between A and B buses in 5-V digital systems. It features direction control (DIR), output-enable (OE), ±6-mA drive strength at 5 V, 14-ns typical propagation delay, and TTL-compatible inputs. It is used in bidirectional data buffering for microcontroller peripheral interfaces and memory expansion subsystems.

For engineers reviewing the SN74HCT645PWR datasheet, SN74HCT645PWR pinout, SN74HCT645PWR application, or SN74HCT645PWR equivalent, key selection criteria include bidirectional bus isolation timing, 3-state output leakage (≤5 µA), operating voltage range (4.5–5.5 V), and TSSOP-20 thermal performance (θ_JA = 83°C/W).

Technical Context

This device implements dual 8-bit bidirectional transceivers with independent DIR and OE controls per bus pair. Logic operation follows true-level TTL-compatible input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2 V) and delivers rail-to-rail CMOS outputs with high-current 3-state capability (±6 mA sink/source at 5 V).

Propagation delay (t_pd) is specified at 14 ns (typ) under 5.5-V/25°C/50-pF conditions, while enable/disable times (t_en/t_dis) are 22 ns/23 ns (typ) - critical for synchronous bus arbitration. Input leakage remains ≤1 µA max across temperature, supporting low-static-power system design.

Key Specifications

Pinout & Package

TSSOP-20 package (PW), 6.5 mm × 4.4 mm footprint, 1.2 mm max height, 0.65 mm lead pitch, moisture sensitivity level 1 (260°C reflow).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT245PW and 74LVTH16245DGGR, the SN74HCT645PWR uniquely integrates direction control into a single pin (DIR) within a 5-V tolerant, pin-compatible TSSOP-20 package - simplifying control logic and preserving legacy 5-V system integrity without voltage translation.

Availability

SN74HCT645PWR is available at Aetrix Electronics and suitable for industrial I/O modules, microcontroller peripheral interfaces, and memory expansion subsystems requiring stable component supply and long-term lifecycle support.

Supply support for SN74HCT645PWR 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 delivering analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74HCT645PWR belongs to TI's HCT logic family - engineered for TTL-compatible operation in 5-V systems with low power, high noise immunity, and robust bus isolation for legacy and upgrade applications.

FAQ

What is the maximum clock/data rate supported by SN74HCT645PWR?

The SN74HCT645PWR does not operate on a clock signal - it is an asynchronous transceiver. Its 14-ns typical propagation delay supports reliable data transfer up to approximately 35 MHz in systems with adequate setup/hold margins. Maximum usable rate depends on bus capacitance, termination, and controller timing constraints - verified per application-specific timing analysis using t_pd, t_en, and t_dis values from the SN74HCT645PWR datasheet.

Can SN74HCT645PWR interface directly with 3.3-V logic devices?

No - the SN74HCT645PWR operates strictly at 4.5–5.5 V and has TTL-compatible input thresholds (V_IH ≥ 2 V). While its outputs may be safely received by many 3.3-V inputs, driving 3.3-V inputs with 5-V logic levels risks overvoltage damage unless the receiving device specifies 5-V tolerance. For mixed-voltage systems, use a dedicated level translator or select a dual-supply transceiver instead of relying on SN74HCT645PWR alone.

How does the DIR pin control data flow direction in SN74HCT645PWR?

In the SN74HCT645PWR, the DIR pin is a logic-level control: when DIR = HIGH, data flows from A-bus inputs to B-bus outputs; when DIR = LOW, data flows from B-bus inputs to A-bus outputs. This single-pin direction control eliminates the need for separate A→B and B→A enable signals, simplifying control logic compared to alternatives like SN74HCT245. The function is defined in the SN74HCT645PWR truth table and applies independently of OE state.

What is the thermal resistance (θ_JA) of SN74HCT645PWR in its TSSOP package?

The SN74HCT645PWR in the PW (TSSOP-20) package has a junction-to-ambient thermal resistance (θ_JA) of 83°C/W, as specified in the Absolute Maximum Ratings table. This value assumes standard JEDEC test board conditions (2-layer board, 1-in² copper pad). Actual thermal performance in end equipment depends on PCB layout, copper area, airflow, and adjacent heat sources - derating is recommended above 70°C ambient for continuous operation.

Is SN74HCT645PWR RoHS compliant and lead-free?

Yes - the SN74HCT645PWR is RoHS compliant and features NiPdAu (NIPDAU) lead finish, as confirmed in TI's Packaging Information Addendum. It meets JEDEC J-STD-020 moisture sensitivity level 1 (MSL-1) and is rated for peak reflow temperatures up to 260°C. Full compliance documentation, including material declarations and test reports, is available through Texas Instruments' official product page for SN74HCT645PWR.