STMicroelectronics 74AC299MTR

Overview

74AC299MTR from STMicroelectronics is an advanced high-speed CMOS 8-bit parallel-in/parallel-out (PIPO) shift register with 3-state outputs and asynchronous clear, operating from 2V to 6V supply. It supports four functional modes-HOLD, SHIFT LEFT, SHIFT RIGHT, and LOAD DATA-via S0/S1 select inputs, delivers 24mA output drive, and achieves 240MHz max clock frequency at 5V. Used in bus-oriented digital systems requiring bidirectional data routing and temporary storage, such as industrial control I/O expansion.

For engineers reviewing the 74AC299MTR datasheet, 74AC299MTR pinout, 74AC299MTR application, or 74AC299MTR equivalent, key selection criteria include its 24mA symmetrical drive capability, 50Ω transmission line compatibility, asynchronous master reset, 8-bit bidirectional shift functionality, and TSSOP-20 package suitability for space-constrained PCB layouts.

Technical Context

The 74AC299 implements a synchronous edge-triggered (LOW-to-HIGH clock) 8-bit register with dual serial paths (SL for left-shift, SR for right-shift) and parallel I/O terminals (A/QA–H/QH) that function as either inputs or 3-state outputs depending on G1/G2 enable states. Mode selection is fully combinational via S0/S1, while CLEAR operates asynchronously and independently of clock or enable signals.

All inputs and outputs feature ESD protection (2kV HBM), and the device uses sub-micron C2MOS technology to achieve low ICC (8µA max at 25°C) and balanced tPLH/tPHL propagation delays. Its 50Ω transmission line driving capability and symmetrical |IOH| = |IOL| = 24mA (min) support clean signal integrity in high-speed digital interconnects without external termination.

Key Specifications

Pinout & Package

TSSOP-20 package: 6.5mm × 4.4mm body, 0.65mm pitch, exposed pad not present, RoHS-compliant, surface-mount compatible.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-bit PIPO shift register applications.

Compared with 74ACT299MTR and SN74LV299APW, the 74AC299MTR offers superior noise immunity (28% VCC), higher drive strength, and guaranteed 2kV ESD protection - making it optimal for industrial environments with noisy power rails and manual handling requirements.

Availability

74AC299MTR is available at Aetrix Electronics and suitable for industrial PLC I/O expansion, digital test equipment data capture, and legacy bus interface adapter designs requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant TSSOP packaging.

Supply support for 74AC299MTR 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 CMOS performance with TTL-compatible drive and noise immunity, targeting industrial control, instrumentation, and legacy-system upgrade applications where reliability and interoperability are critical.

FAQ

What is the minimum pulse width required for the CLEAR input to ensure reliable reset?

The minimum CLEAR pulse width is 5.0ns at VCC = 5.0V, as specified in the AC Electrical Characteristics table. This ensures the asynchronous reset propagates reliably through all eight flip-flops regardless of clock phase or enable state. Pulse widths below this value may result in partial or failed register clearing, especially under worst-case temperature and voltage conditions.

Can the 74AC299MTR operate reliably at 3.3V supply voltage?

Yes - the device is fully specified for VCC = 3.3V ± 0.3V operation, with guaranteed parameters including fMAX = 210MHz (typ.), tPLH/tPHL ≤ 22.0ns, and VIH/VIL thresholds scaled to 30–70% of VCC. All DC and AC characteristics in the datasheet include explicit 3.3V test conditions, confirming robust functionality in mixed-voltage 3.3V/5V systems.

How does the 3-state output enable logic work with G1 and G2 inputs?

G1 and G2 are independent active-low enables: all eight parallel I/O terminals (A/QA–H/QH) enter high-impedance state if *either* G1 *or* G2 is HIGH. Outputs return to active drive only when *both* G1 and G2 are LOW. This dual-enable structure allows fail-safe bus isolation - for example, one enable can be tied to system reset while the other is controlled by software.

Is the 74AC299MTR pinout compatible with the older 74LS299 DIP version?

Yes - the pin assignment, signal names, and functional behavior are identical between 74AC299MTR (TSSOP-20) and 74LS299 (DIP-20), including S0/S1, G1/G2, CLEAR, CLOCK, SL/SR, and all I/O terminals. This allows direct drop-in replacement in existing layouts when migrating from through-hole to surface-mount, provided PCB land patterns accommodate TSSOP-20 dimensions and soldering profiles.