Texas Instruments CD74HCT123MT

Overview

CD74HCT123MT from Texas Instruments is a dual retriggerable monostable multivibrator with independent resets, designed for precise pulse generation and timing control in digital systems. It operates from 4.5V to 5.5V, features Schmitt-trigger inputs on both A and B trigger pins, supports trailing-edge (A) and leading-edge (B) triggering, and delivers buffered Q and Q̅ outputs. It is used in debounce circuits, event timing, and programmable delay generation where temperature-stable pulse widths from external RC networks are required.

For engineers reviewing the CD74HCT123MT datasheet, CD74HCT123MT pinout, CD74HCT123MT application, or CD74HCT123MT equivalent, this page provides verified functional specifications, SOIC-16 package details, real-world use cases in industrial control and instrumentation, and validated alternative parts with documented electrical and timing differences.

Technical Context

The CD74HCT123MT implements two independent monostable multivibrators, each with separate A/B edge-selectable trigger inputs and dedicated reset (R) terminals. Each mono is retriggerable: an active input during an ongoing output pulse extends t_W, while a LOW on R terminates it immediately.

Timing is set externally via R_X and C_X; at V_CC = 5V, t_W ≈ 0.45 × R_XC_X. Input thresholds match LSTTL logic (V_IL ≤ 0.8V, V_IH ≥ 2.0V), ensuring direct compatibility with legacy TTL systems without level-shifting.

Key Specifications

Pinout & Package

CD74HCT123MT is housed in a 16-pin SOIC (Small Outline Integrated Circuit) package, 3.9mm wide, with 1.27mm pitch and JEDEC MS-012 compliant footprint. Thermal resistance θ_JA = 73°C/W enables reliable operation up to 125°C ambient without forced airflow.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual monostable multivibrator applications.

Compared with CD74HCT123MT, SN74HCT123DR offers assured long-term availability and updated quality documentation, while 74HCT123D,653 provides automotive qualification and higher reel quantities - both retain identical timing behavior and pin compatibility but differ in supply chain maturity and environmental rating scope.

Availability

CD74HCT123MT is available at Aetrix Electronics and suitable for industrial control systems, test equipment design, and aerospace subsystems requiring stable component supply across extreme temperature ranges and long product lifecycles.

Supply support for CD74HCT123MT 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

Texas Instruments is a global semiconductor leader specializing in analog and embedded processing technologies, with decades of heritage in high-reliability logic and timing solutions.

The CD74HCT123MT belongs to TI's legacy high-speed CMOS logic family, engineered for robust operation in harsh environments and direct interoperability with legacy TTL systems - targeting industrial automation, defense electronics, and instrumentation markets.

FAQ

What is the maximum operating temperature for CD74HCT123MT?

The CD74HCT123MT is rated for continuous operation from -55°C to +125°C. This extended temperature range is verified per the datasheet's Absolute Maximum Ratings and Operating Conditions tables, making it suitable for deployment in engine compartments, downhole tools, and military-grade electronics where ambient thermal stress exceeds commercial-grade limits. The SOIC package's θ_JA of 73°C/W supports this rating with appropriate PCB copper area.

Can CD74HCT123MT be used with a 3.3V supply?

No, CD74HCT123MT requires a supply voltage between 4.5V and 5.5V. Its HCT logic family is specifically designed for 5V TTL compatibility, with input thresholds (V_IL ≤ 0.8V, V_IH ≥ 2.0V) and output drive characteristics optimized for 5V operation. Using 3.3V violates the minimum V_CC specification and will result in unreliable triggering, degraded noise margins, and potential failure to meet timing parameters - use CD74HC123MT instead for 2V–6V operation.

How do I calculate the output pulse width for CD74HCT123MT?

The nominal output pulse width t_W for CD74HCT123MT is calculated as t_W = 0.45 × R_X × C_X at V_CC = 5V, where R_X is the external timing resistor (minimum 5kΩ) and C_X is the external timing capacitor (minimum 0pF). For example, with R_X = 10kΩ and C_X = 10nF, t_W ≈ 45µs. Actual width varies ±2% between channels and exhibits minor V_CC dependence per the "K factor" curve in the datasheet.

Does CD74HCT123MT support retriggering during an active output pulse?

Yes, CD74HCT123MT is explicitly retriggerable: applying a valid trigger (A or B edge) while Q is HIGH extends the output pulse width by another t_W interval. This behavior is confirmed in the Functional Description and Truth Table sections of the datasheet. Retriggering is subject to minimum retrigger time (t_rT = 76ns max at V_CC = 5V), which must elapse between successive active edges to ensure reliable extension.

What is the purpose of the Schmitt-trigger inputs on CD74HCT123MT?

The Schmitt-trigger inputs on CD74HCT123MT (applied to all A, B, and R pins) provide hysteresis - typically 30% of V_CC - to reject noise and prevent multiple triggering from slow-rising or noisy input signals. This ensures clean, single-shot response even when interfacing with mechanical switches, long traces, or unfiltered sensor outputs, eliminating the need for external RC filtering or debouncing circuitry in many applications.