STMicroelectronics 74ACT161MTR

Overview

74ACT161MTR from STMicroelectronics is a high-speed CMOS synchronous presettable 4-bit binary counter with asynchronous clear, operating at up to 290 MHz (typ.) at 5 V, featuring 24 mA output drive, 50 Ω transmission line compatibility, and pin/function compatibility with standard 74-series 161 counters for use in digital timing and control circuits.

For engineers reviewing the 74ACT161MTR datasheet, 74ACT161MTR pinout, 74ACT161MTR application, or 74ACT161MTR equivalent, this device supports precise clocked counting, cascaded counter chains, parallel data loading, and synchronous reset - critical for state machines, frequency division, and address generation in industrial logic systems.

Technical Context

The 74ACT161MTR implements a 4-bit synchronous binary counter with four distinct operational modes: synchronous reset (via CLEAR), parallel load (via LOAD), count-up (enabled by both PE and TE HIGH), and hold (when either PE or TE is LOW). Its edge-triggered CLOCK input responds only to rising transitions.

All inputs tolerate TTL voltage levels (VIH ≥ 2.0 V, VIL ≤ 0.8 V), and outputs deliver symmetrical sourcing/sinking capability (|IOH| = IOL = 24 mA min) with balanced propagation delays (tPLH ≅ tPHL) and guaranteed 50 Ω line driving - enabling direct interface with legacy TTL, NMOS, and modern CMOS systems without level-shifting.

Key Specifications

Pinout & Package

TSSOP-16 package (4.9 × 6.4 mm body, 0.65 mm pitch), lead-free and RoHS-compliant, optimized for high-density PCB layouts and automated assembly.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous counter applications.

Compared with 74AC161SCX and SN74ACT161N, the 74ACT161MTR uniquely combines TSSOP-16 miniaturization, guaranteed 50 Ω line driving, and 290 MHz operation - making it optimal for space-constrained, high-speed digital control boards requiring signal integrity and industrial temperature support.

Availability

74ACT161MTR is available at Aetrix Electronics and suitable for industrial PLC timing modules, digital panel meter counting, and test equipment frequency dividers requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.

Supply support for 74ACT161MTR 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, specializing in automotive, industrial, and power management ICs with broad analog, digital, and mixed-signal portfolios.

The 74ACT161MTR belongs to ST's advanced high-speed CMOS logic family, designed specifically for replacing legacy TTL counters in noise-sensitive, high-reliability industrial and test equipment applications.

FAQ

Is the 74ACT161MTR pin-compatible with the original 74LS161?

Yes - the 74ACT161MTR maintains identical pin numbering, function mapping, and truth table behavior as the 74LS161, including asynchronous CLEAR, synchronous LOAD, and dual-count-enable (PE/TE) logic. No PCB redesign is needed for drop-in replacement, though decoupling and layout practices should follow CMOS guidelines due to higher speed and lower noise margin.

What is the minimum setup time required for the LOAD input relative to CLOCK?

The LOAD input requires a minimum setup time of 8.5 ns (max) before the rising edge of CLOCK at –40°C to +85°C, per AC specifications. This ensures reliable capture of the parallel data inputs (A–D) into the internal flip-flops without metastability - critical when interfacing with FPGA or microcontroller GPIOs driving LOAD asynchronously.

Can the 74ACT161MTR drive a 50 Ω coaxial cable directly?

Yes - the device is explicitly characterized for 50 Ω transmission line driving capability with symmetrical 24 mA output drive and matched rise/fall times. When terminated properly at the far end, it delivers clean edges without ringing or overshoot, eliminating the need for external series resistors in point-to-point high-speed interconnects.

Does the CARRY OUT signal assert during synchronous reset or parallel load?

No - CARRY OUT remains LOW during asynchronous CLEAR, synchronous LOAD, or HOLD modes. It asserts HIGH only when TE = HIGH and the counter reaches state 15 (QD:QC:QB:QA = 1111) in COUNT UP mode. This behavior ensures predictable cascade chaining without spurious carry assertions during configuration changes.