Texas Instruments SN74HC645N

Overview

SN74HC645N from Texas Instruments is an octal bus transceiver IC designed for asynchronous two-way data communication between parallel buses. It features bidirectional data flow controlled by DIR, 3-state outputs enabled/disabled by OE, operates from 2 V to 6 V, delivers ±6-mA output drive at 5 V, and achieves typical propagation delay of 12 ns - used in microcontroller peripheral interfacing and legacy bus isolation.

For engineers reviewing the SN74HC645N datasheet, SN74HC645N pinout, SN74HC645N application, or SN74HC645N equivalent, this page provides verified functional role, validated timing behavior, confirmed 20-pin PDIP package mapping, and real-world interface use cases - all derived from TI's official SCLS304B datasheet and packaging documentation.

Technical Context

The SN74HC645N implements dual-rail CMOS logic with true high-impedance 3-state outputs, enabling bus contention avoidance during direction switching. Its DIR input selects A→B or B→A data path, while OE independently disables all outputs into high-Z state - supporting hot-swap and shared-bus arbitration.

It meets HC-series logic thresholds (VIH = 3.15 V min at VCC = 4.5 V; VIL = 1.35 V max), supports CL = 50 pF and CL = 150 pF load conditions, and maintains stable operation across –40°C to +85°C ambient temperature with ICC ≤ 80 µA max at 6 V.

Key Specifications

Pinout & Package

SN74HC645N is housed in a 20-pin plastic dual in-line package (PDIP-N), 0.300-inch wide body, with standard through-hole mounting and 0.1-inch pin pitch. Pin 1 is located at the top-left corner adjacent to the notch or dot marking.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC645N, SN74HCT645N offers TTL-compatible inputs at the cost of slightly higher static current, while 74LCX645M delivers superior speed and voltage flexibility but lacks PDIP packaging and requires redesign for 5 V operation.

Availability

SN74HC645N is available at Aetrix Electronics and suitable for industrial control backplanes, microcontroller peripheral expansion, and legacy bus isolation requiring stable component supply, long-term lifecycle support, and RoHS-compliant through-hole assembly.

Supply support for SN74HC645N 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 50 years of innovation in industrial, automotive, and communications markets.

The SN74HC645N belongs to TI's 74HC high-speed CMOS logic family, engineered for robust noise immunity, low power, and seamless compatibility with legacy TTL systems in space-constrained industrial designs.

FAQ

What is the function of the DIR pin on the SN74HC645N?

The DIR (direction) pin on the SN74HC645N determines data flow direction: when DIR is HIGH, data passes from the A bus (pins 2–9) to the B bus (pins 13–20); when DIR is LOW, data flows from B to A. This single-control bidirectional capability eliminates the need for separate transmit/receive buffers in the SN74HC645N design.

Can the SN74HC645N operate at 3.3 V supply voltage?

Yes, the SN74HC645N is fully specified to operate at 3.3 V, as confirmed by its 2 V to 6 V supply range and guaranteed VIH/VIL thresholds (e.g., VIH = 2.31 V min at VCC = 3.3 V per TI's recommended operating conditions). The SN74HC645N maintains full 3-state functionality and 12 ns typical propagation delay at this voltage.

What is the maximum capacitive load the SN74HC645N can drive reliably?

The SN74HC645N is characterized for CL = 50 pF and CL = 150 pF loads, with timing parameters explicitly published for both conditions in the official datasheet. At VCC = 6 V, tpd remains within 29 ns (max) even at 150 pF, confirming the SN74HC645N's suitability for driving longer traces or multiple fanouts without added buffering.

Does the SN74HC645N have built-in ESD protection?

The SN74HC645N incorporates standard CMOS input protection diodes rated for ±20 mA clamp current (per Absolute Maximum Ratings), providing basic handling-level ESD robustness. However, it does not include enhanced system-level ESD structures (e.g., IEC 61000-4-2 compliant), so external TVS devices are recommended in harsh environments - a design consideration specific to the SN74HC645N's implementation.

Is the SN74HC645N pin-compatible with other 74HC-series transceivers like the SN74HC245?

No, the SN74HC645N is not pin-compatible with SN74HC245. While both are octal transceivers, SN74HC245 uses separate A→B and B→A control (two OE inputs), whereas SN74HC645N uses DIR + single OE and has different pin assignments (e.g., DIR on pin 1 vs. no DIR on SN74HC245). Board layout and firmware logic must be redesigned to substitute SN74HC645N for SN74HC245.