STMicroelectronics 74AC245B

Overview

74AC245B from STMicroelectronics is an advanced high-speed CMOS octal bus transceiver with 3-state non-inverting outputs, designed for bidirectional asynchronous data bus communication. It features 4.5 ns typical propagation delay at 5 V, ±24 mA symmetrical output drive, and operates across 2 V to 6 V supply range. Used in legacy industrial control backplanes and memory-mapped peripheral interfaces where direction-controlled bus isolation is required.

For engineers reviewing the 74AC245B datasheet, 74AC245B pinout, 74AC245B application, or 74AC245B equivalent, key selection criteria include directional control logic (DIR), 3-state enable timing (tPZL/tPLZ ≤ 9.0 ns at 5 V), rail-to-rail input thresholds (VIH/VIL = 2.1/0.9 V @ 3 V), and DIP-20 package compatibility with 74-series footprints.

Technical Context

The 74AC245B implements dual-bus bidirectional data flow controlled by a single DIR input and a separate active-low G (output enable) signal. Its 3-state outputs provide high-impedance isolation when disabled, with leakage current ≤ 10 µA over full temperature range (–55°C to +125°C).

It uses sub-micron C2MOS technology to achieve balanced tPLH ≅ tPHL propagation delays and symmetrical |IOH| = |IOL| = 24 mA (min) drive strength into 50 Ω transmission lines - enabling clean signal integrity without external termination in point-to-point bus designs.

Key Specifications

Pinout & Package

74AC245B is supplied in a 20-pin plastic DIP (Dual In-line Package) with 0.3-inch body width and 0.1-inch lead pitch, compliant with JEDEC MS-001. Pin 1 is marked by a notch or dot; pin numbering follows standard DIP convention (counterclockwise from top-left corner).

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74ACT245 and SN74LVC245A, the 74AC245B uniquely supports 2–6 V operation with 2 kV ESD protection and DIP-20 through-hole mounting - making it the only option for legacy-replacement, mixed-voltage, or repair-focused applications requiring mechanical robustness and wide supply flexibility.

Availability

74AC245B is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy memory expansion systems, programmable logic interfacing, and test equipment bus coupling requiring stable component supply and long-term obsolescence mitigation.

Supply support for 74AC245B 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, digital, and mixed-signal ICs for automotive, industrial, and consumer markets.

The 74AC logic family was developed to deliver high-speed, low-power, and latch-up-immune CMOS alternatives to legacy 74LS and 74F devices - specifically targeting industrial control, instrumentation, and retro-system upgrades.

FAQ

What is the maximum clock/data toggle rate supported by the 74AC245B?

The 74AC245B has a typical propagation delay of 4.5 ns at 5 V, allowing reliable operation up to approximately 100 MHz in point-to-point configurations with matched 50 Ω transmission lines. AC performance is specified with CL = 50 pF and RL = 500 Ω; actual usable frequency depends on trace length, loading, and termination.

Can the 74AC245B operate safely at 3.3 V while interfacing with 5 V peripherals?

Yes - the 74AC245B is fully specified from 2 V to 6 V and tolerates 5 V inputs at any supply voltage within that range. Its VIH threshold at 3.3 V is 2.1 V (min), ensuring reliable recognition of 5 V logic HIGH signals without level shifting.

Is the 74AC245B pin-compatible with standard 74LS245 devices?

Yes - the 74AC245B maintains identical pinout, function mapping, and logic behavior (non-inverting, DIR/G control) as the 74LS245 and 74F245, enabling drop-in replacement in existing PCB layouts with improved speed, lower power, and higher noise immunity.

Does the 74AC245B require external pull-up or pull-down resistors on its 3-state outputs?

No - floating bus terminals during HIGH-Z must be externally held HIGH or LOW per datasheet guidance, but this is a system-level requirement, not a device limitation. The IC itself does not integrate pull resistors; external biasing is needed only if bus nodes lack defined termination in the application circuit.