onsemi MC74ACT640DWR2G

Overview

MC74ACT640DWR2G from onsemi is an octal 3-state inverting bus transceiver for asynchronous bidirectional data transfer between two 8-bit buses. It operates at 4.5–5.5 V, supports ±24 mA output drive, features TTL-compatible inputs, and uses a single T/R control line to select direction (A→B or B→A) with independent OE enable. It is used in industrial backplane interfaces requiring isolated bus communication.

For engineers reviewing the MC74ACT640DWR2G datasheet, pinout, applications, or equivalent options, key selection criteria include bidirectional 3-state control timing (tPLH/tPHL ≤ 8.5 ns), output drive capability (IOL = 24 mA), operating temperature range (−40°C to +85°C), and SOIC-20W Pb-free packaging compliance.

Technical Context

The MC74ACT640DWR2G implements a dual-bus, direction-controlled transceiver architecture with separate Output Enable (OE) and Transmit/Receive (T/R) logic inputs. Its 3-state outputs on both A and B sides allow dynamic bus isolation, and its TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) ensure interoperability with legacy 5 V logic families.

Propagation delays are tightly specified: tPLH/tPHL ≤ 8.5 ns (max) at VCC = 5.0 V and CL = 50 pF; output enable/disable times (tPZH/tPLZ/tPHZ/tPLZ) are ≤ 11.0 ns (max). The device meets JEDEC AC/DC specifications for ACT-family speed and drive strength while maintaining latch-up immunity (±100 mA) per JESD78.

Key Specifications

Pinout & Package

MC74ACT640DWR2G is housed in a 20-lead SOIC wide-body (SOIC-20W, Case 751D) package with 1.27 mm pitch, 12.8 mm × 7.5 mm body size, and Pb-free finish (G suffix).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74ACT640N and MC74LCX640DT, the MC74ACT640DWR2G uniquely combines 5 V TTL compatibility, SOIC-20W SMT packaging, and Pb-free compliance - making it the preferred choice for industrial 5 V backplane upgrades requiring RoHS-conformant, automated assembly.

Availability

MC74ACT640DWR2G is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy system bus extensions, microcontroller peripheral multiplexing, and modular I/O subsystems requiring stable component supply and long-term manufacturability.

Supply support for MC74ACT640DWR2G 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The MC74ACT640DWR2G belongs to onsemi's Advanced CMOS (ACT) logic family, engineered specifically for high-speed, low-noise 5 V digital interfacing in industrial control and legacy system modernization.

FAQ

What is the maximum operating frequency supported by the MC74ACT640DWR2G?

The MC74ACT640DWR2G does not specify a maximum clock frequency, as it is an asynchronous transceiver. Its timing is governed by propagation delay (tPLH/tPHL ≤ 8.5 ns) and enable/disable times (≤ 11.0 ns). In practice, it reliably supports bus handshaking up to 10 MHz with adequate setup/hold margins. For synchronous protocols, system-level timing analysis must include trace delays and load capacitance - the MC74ACT640DWR2G itself imposes no hard frequency ceiling beyond its AC characteristics.

Is the MC74ACT640DWR2G compatible with 3.3 V logic inputs?

No, the MC74ACT640DWR2G is not guaranteed compatible with 3.3 V logic inputs. Its input thresholds require VIH ≥ 2.0 V (min) and VIL ≤ 0.8 V (max) at VCC = 5.0 V, which aligns with TTL but exceeds typical 3.3 V CMOS high-level thresholds (~2.0 V is marginal). Driving it directly from 3.3 V outputs risks undefined switching behavior. Use level-shifting circuitry or select the MC74LCX640DT variant if interfacing with 3.3 V systems.

Does the MC74ACT640DWR2G require external pull-up or pull-down resistors on unused inputs?

Yes, unused inputs on the MC74ACT640DWR2G must not be left floating. Per the datasheet (Note 6), all inputs - including T/R and OE - must be tied to a valid logic level (VCC or GND) to prevent increased ICC, noise susceptibility, or erratic output behavior. For OE, tying to VCC disables outputs; for T/R, tying to VCC fixes A→B direction. Pull-up/pull-down resistors (typically 10 kΩ) are acceptable, but direct connection is preferred for lowest noise.

What is the thermal resistance (θJA) of the MC74ACT640DWR2G in its SOIC-20W package?

According to the official onsemi datasheet, the MC74ACT640DWR2G in SOIC-20W (Case 751D) has a junction-to-ambient thermal resistance (θJA) of 96°C/W, measured per JESD51-7. This value assumes standard JEDEC 2-layer board conditions. Actual thermal performance depends on PCB copper area, airflow, and adjacent heat sources - for continuous 24 mA output loading, keep ambient temperature below +70°C or add localized copper pour to reduce effective θJA.

Can the MC74ACT640DWR2G be used in place of the MC74ACT245?

No, the MC74ACT640DWR2G cannot directly replace the MC74ACT245. While both are octal transceivers, the MC74ACT640DWR2G is inverting and uses separate T/R and OE controls, whereas the MC74ACT245 is non-inverting with a single direction pin (DIR) and OE. Their truth tables, pinouts, and logic polarity differ fundamentally. Substitution would require PCB redesign and firmware logic inversion - the MC74ACT640DWR2G is not a functional or pin-compatible alternative to the MC74ACT245.