Texas Instruments CD74HCT123M

Overview

CD74HCT123M 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 output pulse widths from ~40 µs (RX = 10 kΩ, CX = 10 nF), and delivers buffered Q and Q̅ outputs. It is used in edge-triggered delay circuits, debouncing switches, and programmable one-shot timers.

For engineers reviewing the CD74HCT123M datasheet, CD74HCT123M pinout, CD74HCT123M application, or CD74HCT123M equivalent, this page provides verified functional context, validated SOIC-16 package details, confirmed HCT logic compatibility with LSTTL inputs, real-world timing behavior under -55°C to +125°C, and two technically documented alternative parts for design flexibility.

Technical Context

The CD74HCT123M implements two independent monostable multivibrators, each with separate A (trailing-edge) and B (leading-edge) trigger inputs, individual reset (R) terminals, and buffered complementary outputs (Q/Q̅). Its retriggerable architecture allows extension of the output pulse width upon successive valid triggers before timeout.

Timing is externally controlled via resistor RX and capacitor CX, with pulse width calculated as t_W = 0.45 × R_XC_X at V_CC = 5 V. The device includes Schmitt-trigger input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V), ensuring noise immunity and consistent triggering regardless of input rise/fall times.

Key Specifications

Pinout & Package

CD74HCT123M is housed in a 16-pin Small Outline Integrated Circuit (SOIC) package per JEDEC MS-012, with 1.27 mm pitch, 10.0–10.4 mm body width, and 7.4–8.2 mm length. Thermal resistance θ_JA = 73°C/W enables operation up to 125°C ambient with moderate power dissipation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HCT123M, SN74HCT123DR offers identical performance and drop-in replacement assurance, while MC74HC123ADR2G trades LSTTL compatibility for broader voltage operation - making it viable only in fully CMOS-specified environments.

Availability

CD74HCT123M is available at Aetrix Electronics and suitable for industrial control panels, aerospace telemetry modules, and automotive body electronics requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for CD74HCT123M 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, embedded processing, and logic solutions, with over 90 years of innovation in high-reliability IC design.

The CD74HCT123M belongs to TI's legacy 74HCT logic family, engineered for robust, pin-compatible replacements of bipolar TTL in industrial, military, and space-grade timing applications.

FAQ

What is the minimum external resistor value supported by CD74HCT123M?

The CD74HCT123M specifies a typical minimum external timing resistor (R_X) of 5 kΩ. Using lower values may cause excessive current draw, timing inaccuracies, or reduced output drive capability. Always pair R_X with C_X ≥ 0 pF and verify pulse width using t_W = 0.45 × R_XC_X at V_CC = 5 V. For precision timing, select 1% metal-film resistors and NP0/C0G capacitors.

Can CD74HCT123M operate with a 3.3 V supply?

No, CD74HCT123M is specified exclusively for 4.5 V to 5.5 V operation. Its HCT logic family requires V_CC ≥ 4.5 V to guarantee correct LSTTL input compatibility (V_IH ≥ 2.0 V, V_IL ≤ 0.8 V) and output drive strength. For 3.3 V systems, consider HC-family alternatives like CD74HC123M - but note that those lack native TTL input compatibility and require level-shifting if interfacing with 5 V sources.

How does the retriggering behavior of CD74HCT123M differ from non-retriggerable monostables?

Unlike non-retriggerable monostables that ignore subsequent triggers until the initial pulse completes, CD74HCT123M extends its output pulse width upon each valid A or B edge occurring before timeout. This allows dynamic pulse stretching - e.g., holding an enable signal active while a sensor remains asserted. Retriggering requires meeting the minimum retrigger time (t_rT = 76 ns max at -55°C to +125°C) to avoid metastability.

Is CD74HCT123M pin-compatible with CD74HC123M?

Yes, CD74HCT123M and CD74HC123M share identical SOIC-16 pinouts, terminal functions, and package dimensions. However, they differ electrically: CD74HCT123M accepts LSTTL input levels (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) and operates only from 4.5–5.5 V, whereas CD74HC123M supports 2–6 V but requires CMOS-compatible inputs (V_IH ≥ 3.15 V at 4.5 V). Interchange requires verifying driver compatibility.

What is the maximum recommended external capacitor value for stable operation of CD74HCT123M?

The CD74HCT123M datasheet does not specify a maximum C_X value, but practical limits arise from leakage current, timing accuracy degradation, and propagation delay increase. For stable operation across -55°C to +125°C, TI recommends C_X ≤ 100 nF with low-leakage dielectrics (e.g., NP0/C0G or film). Larger values (>1 µF) risk significant pulse width drift due to capacitor ESR and temperature coefficient effects - always validate with actual board-level testing.