onsemi MC74AC245MELG

Overview

MC74AC245MELG from onsemi is an octal bidirectional transceiver with 3-state inputs/outputs, designed for bus-oriented data transfer between two 8-bit parallel buses. It supports 2.0–6.0 V supply operation, delivers ±24 mA output drive at both A and B ports, and uses active-HIGH Transmit/Receive (T/R) and active-HIGH Output Enable (OE) control logic. It is commonly deployed in microcontroller system bus buffering, memory expansion interfaces, and industrial I/O module data routing.

For engineers reviewing the MC74AC245MELG datasheet, pinout, applications, or equivalent options, key selection considerations include its 20-pin SOIC-WB package, bidirectional flow control via T/R input, 3-state output isolation, 5.0 V typical propagation delay of 3.5–6.5 ns, and compatibility with AC-level CMOS logic families across −40°C to +85°C ambient operation.

Technical Context

The MC74AC245MELG implements eight independent non-inverting bidirectional buffers, each with symmetrical current-sinking (24 mA) and current-sourcing (24 mA) capability at both A and B ports. Direction is controlled by a single TTL-compatible T/R input: logic HIGH enables A→B data flow; logic LOW enables B→A flow.

Output state is managed by the OE input: logic HIGH forces all A and B terminals into high-impedance (Hi-Z), effectively isolating both buses. The device operates within a 2.0–6.0 V VCC range, exhibits input thresholds referenced to VCC (VIH = 2.1 V min @ 3.0 V, 3.15 V min @ 4.5 V), and maintains guaranteed VOL ≤ 0.44 V @ 24 mA sink load.

Key Specifications

Pinout & Package

MC74AC245MELG is housed in a 20-pin SOIC-Wide Body (SOIC-20W) package per case 751D, with 0.300-inch body width, 1.27 mm pitch, and Pb-free (RoHS-compliant) finish.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC245APWR and 74ABT245N, the MC74AC245MELG uniquely balances wide supply range (2.0–6.0 V), industrial temperature rating, and SOIC-WB mechanical stability-making it optimal for mixed-voltage industrial controllers where layout flexibility and long-term component availability matter more than ultra-low power or sub-3 ns latency.

Availability

MC74AC245MELG is available at Aetrix Electronics and suitable for industrial PLC backplane interfaces, microcontroller memory expansion systems, and automotive body control modules requiring stable component supply across extended product lifecycles.

Supply support for MC74AC245MELG 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 focused on energy-efficient electronics, delivering silicon solutions for automotive, industrial, cloud, medical, and IoT applications.

The MC74AC245MELG belongs to onsemi's legacy AC logic family, engineered for robust bus interfacing in industrial control, instrumentation, and legacy system upgrades where wide VCC tolerance and proven reliability are prioritized over ultra-low power consumption.

FAQ

What is the recommended operating voltage range for MC74AC245MELG?

The MC74AC245MELG is specified for continuous operation from 2.0 V to 6.0 V VCC. At 3.0 V, VIH is guaranteed ≥2.1 V; at 4.5 V, VIH ≥3.15 V. This range allows direct use in mixed-voltage systems-for example, connecting a 3.3 V microcontroller to a 5 V peripheral bus without level shifters. Operation outside this range may cause functional failure or permanent damage.

How does the T/R input control data direction in MC74AC245MELG?

In MC74AC245MELG, the T/R input is active-HIGH: when T/R = HIGH, data flows from A-port inputs to B-port outputs (A→B); when T/R = LOW, data flows from B-port inputs to A-port outputs (B→A). This single-pin control eliminates the need for separate transmit/receive enable signals, simplifying bus arbitration logic in master-slave architectures.

Can MC74AC245MELG drive standard 50 pF loads at 5 V while meeting timing specs?

Yes. MC74AC245MELG guarantees tPLH/tPHL ≤ 6.5 ns (max) at VCC = 5.0 V and CL = 50 pF, with typical values of 3.5 ns. Its ±24 mA output drive ensures clean signal edges into 50 pF loads, satisfying setup/hold timing for common 8-bit peripherals like SRAM, EPROM, and LCD controllers operating up to ~100 MHz effective bus rates.

Is MC74AC245MELG pin-compatible with MC74ACT245 variants?

No. While MC74AC245MELG and MC74ACT245 share identical pinout and package (SOIC-20W), their input thresholds differ: MC74ACT245 has TTL-compatible VIH/VIL (2.0 V/0.8 V @ 5 V), whereas MC74AC245MELG uses CMOS thresholds (3.15 V/1.35 V @ 4.5 V). Swapping them may cause logic misreads unless the driving source meets the stricter AC-level input requirements.

What is the maximum junction temperature and thermal resistance for MC74AC245MELG in SOIC-20W?

The MC74AC245MELG has a maximum junction temperature (TJ) of 140°C and a junction-to-ambient thermal resistance (θJA) of 96°C/W in SOIC-20W package. Under worst-case conditions (6.0 V, all outputs sinking 24 mA), power dissipation remains below 200 mW-well within safe thermal limits for standard PCB layouts without heatsinking.