Texas Instruments CD74HCT423E

Overview

CD74HCT423E 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 4.5 V to 5.5 V, 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 industrial control logic, debounce circuits, and programmable delay generators where reset-controlled pulse termination is required.

For engineers reviewing the CD74HCT423E datasheet, CD74HCT423E pinout, CD74HCT423E application, or CD74HCT423E equivalent, this page provides verified timing parameters, validated pin functions, real-world use cases in edge-triggered timing systems, and confirmed drop-in alternatives for legacy design refreshes and supply continuity planning.

Technical Context

The CD74HCT423E implements two independent monostable multivibrators, each with separate A (trailing-edge), B (leading-edge), and R (active-low reset) inputs. Pulse width is externally set via resistor RX and capacitor CX, with t_W = 0.45·R_XC_X at V_CC = 5 V. Unlike the '123 family, the '423 variant does not support negative-to-positive reset pulse triggering - its reset is strictly active-low level-sensitive.

Each monostable is fully retriggerable: a new trigger during an ongoing output pulse extends t_W, while a LOW on R terminates the pulse immediately. Inputs include Schmitt-trigger hysteresis for noise immunity, and outputs are CMOS-compatible with TTL-level input logic compatibility (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V).

Key Specifications

Pinout & Package

CD74HCT423E is housed in a 16-pin plastic dual in-line package (PDIP-N), with 0.300-inch body width and standard through-hole mounting. Pin spacing is 0.100 inch, and the package complies with JEDEC MS-001.

Key Features

Applications

Equivalent & Alternatives

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

Compared with CD74HCT123E and SN74HCT123N, the CD74HCT423E offers simplified reset control via level-sensitive input - reducing external logic needed for reset synchronization while maintaining full retriggerability and timing precision across extreme temperatures.

Availability

CD74HCT423E is available at Aetrix Electronics and suitable for industrial control systems, automotive body electronics, and aerospace timing modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for CD74HCT423E 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 solutions, with decades of heritage in high-reliability logic and timing products.

The CD74HCT423E belongs to TI's legacy HCT logic family, engineered for seamless integration into mixed-signal systems requiring TTL-compatible inputs, low-power CMOS operation, and robust performance across harsh environmental conditions.

FAQ

What is the minimum external resistor value for stable operation of the CD74HCT423E?

The CD74HCT423E requires a minimum external timing resistor R_X of 5 kΩ for stable pulse width generation and reliable monostable behavior across the full -55 °C to +125 °C temperature range. Using lower values may cause timing inaccuracy, increased propagation delay variation, or failure to trigger reliably, especially at temperature extremes. Always verify R_X selection against the target t_W and operating conditions using the formula t_W = 0.45·R_XC_X.

Can the CD74HCT423E be used with a 3.3 V supply?

No, the CD74HCT423E is not rated for 3.3 V operation. Its HCT logic family requires a supply voltage of 4.5 V to 5.5 V to guarantee TTL-compatible input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) and specified AC/DC performance. For 3.3 V systems, consider the CD74HC423E (HC family, 2 V–6 V) or redesign with level-shifting circuitry - but note that HC variants lack native TTL input compatibility.

How does the reset functionality differ between CD74HCT423E and CD74HCT123E?

The CD74HCT423E uses a level-sensitive active-low reset (R pin): holding R LOW terminates the output pulse immediately and prevents new triggers until R returns HIGH. In contrast, the CD74HCT123E supports both level-sensitive and negative-to-positive edge-triggered reset - allowing synchronous reset assertion aligned to a clock edge. This makes CD74HCT123E preferable in clock-domain-crossing scenarios, while CD74HCT423E simplifies reset control in level-driven systems.

What is the maximum recommended external capacitance for the CD74HCT423E timing network?

The CD74HCT423E datasheet does not specify a maximum external capacitance C_X, but practical limits arise from leakage current, board parasitics, and timing accuracy. For stable operation across -55 °C to +125 °C, TI recommends C_X ≤ 100 µF when paired with R_X ≥ 5 kΩ. Larger capacitors increase sensitivity to dielectric absorption and leakage, potentially causing pulse width drift or failure to trigger at temperature extremes. Always use low-leakage film or ceramic capacitors for precision timing.

Does the CD74HCT423E support simultaneous triggering of both monostables?

Yes, the CD74HCT423E supports independent and simultaneous triggering: applying valid edges to 1A/1B and 2A/2B concurrently initiates both monostables, each generating its own Q/Q̅ output with timing governed by its dedicated R_X/C_X network. No internal coupling or arbitration exists between channels - they operate fully autonomously, enabling dual-channel timing such as complementary PWM generation or staggered event sequencing.