Texas Instruments CD74HC423M

Overview

CD74HC423M 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 2V to 6V, 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. Its external RC timing network enables adjustable output pulse widths down to sub-microsecond resolution - used in debounce circuits, event timing, and programmable delay generators.

For engineers reviewing the CD74HC423M datasheet, CD74HC423M pinout, CD74HC423M application, or CD74HC423M equivalent, this page provides verified timing parameters, SOIC-16 package details, reset behavior distinctions versus '123 variants, thermal derating guidance, and validated alternatives for industrial control, test equipment, and legacy logic upgrades requiring wide temperature operation (-55°C to +125°C).

Technical Context

The CD74HC423M implements two independent monostable multivibrators, each with separate A/B edge-selectable triggers and dedicated reset (R) inputs. Unlike the '123 family, the '423 variant does not support negative-to-positive reset pulse triggering - its reset is active-low and terminates the output pulse immediately when asserted.

Timing is set externally via resistor RX and capacitor CX, with pulse width calculated as t_W = 0.45·R_XC_X at V_CC = 5V. Minimum R_X is 5kΩ; C_X can be 0pF. Propagation delays (e.g., 64ns max A→Q at 4.5V, 50pF load) and retrigger time (76ns min at -55°C to +125°C) are fully characterized across the full temperature range.

Key Specifications

Pinout & Package

CD74HC423M is housed in a 16-pin SOIC (D) package, 7.5mm width, 1.75mm height, with standard 1.27mm pitch. Pin 1 is marked by a notch or dot; device orientation follows JEDEC MS-012.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HC123M, CD74HC423M removes reset-edge sensitivity for simplified control logic, while SN74LV123ADR trades industrial temperature range for improved speed and drive in commercial-grade 3.3V applications - making CD74HC423M the optimal choice for ruggedized, reset-simplified timing in harsh environments.

Availability

CD74HC423M is available at Aetrix Electronics and suitable for industrial control panels, aerospace avionics test fixtures, and automotive engine management modules requiring stable component supply across extreme temperature cycles and long product lifecycles.

Supply support for CD74HC423M 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 delivering analog and embedded processing solutions for industrial, automotive, and communications markets.

The CD74HC423M belongs to TI's legacy HC logic family, engineered for robust, wide-temperature digital timing in mission-critical systems where reliability outweighs ultra-high speed.

FAQ

What distinguishes CD74HC423M from CD74HC123M?

The CD74HC423M differs from CD74HC123M solely in reset behavior: CD74HC423M accepts only active-low reset pulses, while CD74HC123M also responds to negative-to-positive transitions on the reset pin. All other electrical, timing, and pinout specifications are identical. This makes CD74HC423M simpler to interface with standard push-button or logic-gated reset sources.

Can CD74HC423M operate at 3.3V supply voltage?

Yes, CD74HC423M is fully specified for 2V to 6V operation, including 3.3V. At V_CC = 3.3V, input thresholds scale proportionally (VIH ≈ 2.3V, VIL ≈ 1.0V), and propagation delays increase modestly versus 5V - typical t_PLH is 90ns max at 3.3V/50pF. No level-shifting is required for interfacing with 3.3V microcontrollers.

How is output pulse width calculated for CD74HC423M?

Output pulse width t_W for CD74HC423M is calculated as t_W = 0.45 × R_X × C_X, where R_X is the external timing resistor (min 5kΩ) connected between V_CC and the RXCX pin, and C_X is the external timing capacitor (0pF minimum) connected between the CX pin and GND. This formula applies at V_CC = 5V; a "K factor" correction is provided in the datasheet for other voltages.

Does CD74HC423M support retriggering during an active output pulse?

Yes, CD74HC423M is explicitly retriggerable: applying a valid trigger (A or B edge) before the current output pulse expires extends the pulse width by another t_W interval. Retriggering is subject to a minimum inter-pulse interval (t_rT = 76ns max at -55°C to +125°C) to ensure reliable internal state capture - verified in the switching specifications table.

What is the maximum recommended external capacitor value for stable timing with CD74HC423M?

The CD74HC423M datasheet does not specify an absolute maximum C_X, but practical stability limits arise from leakage and parasitic effects. For reliable operation across -55°C to +125°C, ceramic or film capacitors ≤100nF are recommended. Larger values (e.g., 1µF) may cause timing drift or failure to trigger due to increased dielectric absorption and leakage - TI's application notes advise limiting C_X to 100nF unless validated per application.