onsemi MC74HC640ADT

Overview

MC74HC640ADT from ON Semiconductor (formerly Motorola) is an octal 3-state inverting transceiver IC used for bidirectional asynchronous data bus communication between two independent systems. It features active-low Output Enable (OE), direction control (DIR), 2–6 V operating voltage, ±7.8 mA output drive at 6 V, and high-impedance I/O isolation. It is commonly deployed in industrial backplane interfaces and legacy microprocessor bus expansion.

For engineers reviewing the MC74HC640ADT datasheet, pinout, applications, or equivalent options, key selection considerations include its inverting transceiver logic, 20-pin SOIC-DW package, JEDEC-compliant 3-state timing, and compatibility with CMOS/NMOS/TTL loads across –55°C to +125°C operation.

Technical Context

The MC74HC640ADT implements dual 8-bit bidirectional data paths with inversion on both A→B and B→A transmission, controlled by a single DIR pin and an active-low OE pin. Its silicon-gate CMOS architecture ensures low static current (≤1 µA input leakage) and high noise immunity while maintaining LSTTL-compatible drive strength (15 LSTTL loads).

Propagation delays are voltage- and temperature-dependent: t_PLH/t_PHL = 13 ns typical at V_CC = 6 V, 25°C; t_PLZ/t_PHZ = 19 ns under same conditions. All I/O pins support ±0.5 V beyond supply rails per JEDEC Std. 7A, with maximum I/O capacitance of 15 pF in 3-state mode.

Key Specifications

Pinout & Package

MC74HC640ADT is housed in a 20-pin SOIC package (case 751D–04, DW suffix), 7.5 mm × 12.8 mm body, 1.27 mm pitch, with GND on Pin 10 and V_CC on Pin 20.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC640N and 74VHC640M, the MC74HC640ADT offers optimal balance of wide supply range (2–6 V), industrial temperature support, and SOIC packaging - making it the preferred choice for ruggedized, mixed-voltage, surface-mount bus interface designs.

Availability

MC74HC640ADT is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy microprocessor bus expansion, automotive ECU diagnostics, and programmable logic controller I/O modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for MC74HC640ADT 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

ON Semiconductor (formerly Motorola Semiconductor) is a global leader in high-performance silicon-gate CMOS logic, power management, and analog solutions, serving automotive, industrial, and communications markets.

The MC74HC640ADT belongs to the HC High-Speed CMOS Logic family, designed specifically for robust, low-power, bidirectional bus interfacing in electrically noisy and thermally demanding environments.

FAQ

What logic family does the MC74HC640ADT belong to, and how does it differ from LS-TTL?

The MC74HC640ADT belongs to the high-speed silicon-gate CMOS (HC) logic family. Unlike LS-TTL, it draws significantly less quiescent current (µA vs. mA), operates over a wider voltage range (2–6 V vs. 4.75–5.25 V), exhibits higher noise immunity, and provides symmetrical output drive capability. It is pinout-compatible with LS640 but requires no pull-up resistors for LSTTL interfacing when used with appropriate biasing.

Does the MC74HC640ADT support non-inverting data transfer?

No, the MC74HC640ADT performs inversion on both A→B and B→A data paths - this is inherent to its internal gate structure and cannot be disabled. If non-inverting transceivers are required, alternatives such as MC74HC245ADT must be selected. The MC74HC640ADT's inversion is consistent and predictable, simplifying timing analysis in systems where polarity is accounted for in firmware or layout.

What is the maximum capacitive load the MC74HC640ADT can drive reliably?

The MC74HC640ADT is characterized for CL = 50 pF in AC specifications, with propagation delays and transition times guaranteed under that condition. While it can drive higher loads, performance degrades linearly: t_PD increases ~0.2 ns/pF, and t_TT increases ~0.15 ns/pF beyond 50 pF. For loads exceeding 75 pF, use of series termination or buffer staging is recommended to maintain signal integrity.

Can unused I/O pins on the MC74HC640ADT be left floating?

No. Unused inputs must be tied to a valid logic level - either V_CC or GND - to prevent metastability, excessive current draw, or oscillation due to floating CMOS gates. Unused outputs may be left open only when the device is in 3-state mode (OE = HIGH); otherwise, they must be terminated to avoid contention. This requirement is explicitly stated in the Motorola datasheet for MC74HC640ADT.

Is the MC74HC640ADT RoHS compliant and lead-free?

Yes, the MC74HC640ADT (DW suffix) is manufactured in a RoHS-compliant, lead-free SOIC package per ON Semiconductor's product change notification PCN-1205. It meets J-STD-609 Category 1 marking requirements and contains ≤0.1 wt% lead by homogeneous material. Full compliance documentation, including Sb, Br, Hg, Cd, Pb, and phthalate test reports, is available upon request from Aetrix Electronics.