NXP Semiconductors 74HCT423D,118

Overview

74HCT423D,118 from NXP Semiconductors is a dual retriggerable monostable multivibrator with independent reset inputs, designed for precise pulse generation and extension in digital timing circuits. It features Schmitt-trigger inputs on A/B trigger pins, operates from 4.5 V to 5.5 V, supports −40 °C to +125 °C ambient range, and delivers output pulse widths scalable from nanoseconds to hundreds of microseconds via external R_EXT/C_EXT. It is used in debounce circuits, event stretching, and programmable delay generators.

For engineers reviewing the 74HCT423D,118 datasheet, 74HCT423D,118 pinout, 74HCT423D,118 application, or 74HCT423D,118 equivalent, this device offers verified retriggerable timing control, direct active-LOW reset termination, dual independent channels, JEDEC 7A compliance, and SO16 packaging suitable for industrial-grade signal conditioning and logic timing systems.

Technical Context

The 74HCT423D,118 implements two independent CMOS monostable multivibrators, each with separate negative-edge (nA) and positive-edge (nB) trigger inputs, active-LOW reset (nRD), and complementary outputs (nQ/nQ). Its retriggerable architecture allows indefinite pulse extension by successive edge triggers before timeout - unlike non-retriggerable variants such as the 74HCT123.

Timing is externally set via resistor-capacitor networks connected to nREXT/CEXT and nCEXT pins; minimum pulse width is defined by R_EXT = 2 kΩ to 1000 kΩ and C_EXT with no upper capacitance limit. Propagation delays are specified at 22–77 ns (V_CC = 4.5–5.5 V), and all inputs except nRD include Schmitt-trigger hysteresis for noise immunity on slow-rising signals.

Key Specifications

Pinout & Package

74HCT423D,118 is supplied in a plastic small outline package (SO16), 16-pin, 3.9 mm body width (SOT109-1), with gull-wing leads and standard JEDEC MO-118 footprint. Pin 1 is marked by a notch or index area; the package is RoHS-compliant and rated for reflow soldering per J-STD-020.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HCT423D,118, the 74HCT123D,118 offers simpler single-shot behavior but forfeits pulse extension, while SN74LV423DR trades Schmitt-trigger robustness for wider V_CC range and faster response - making 74HCT423D,118 optimal for industrial debounce and retrigger-critical timing where input integrity is uncertain.

Availability

74HCT423D,118 is available at Aetrix Electronics and suitable for industrial control panels, automotive body electronics, and test equipment requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for 74HCT423D,118 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

NXP Semiconductors is a global semiconductor company headquartered in Eindhoven, Netherlands, specializing in secure connectivity solutions for automotive, industrial, and IoT applications.

The 74HCT423D,118 belongs to NXP's legacy HC/HCT logic family, engineered for robust 5 V TTL-compatible operation with enhanced noise immunity and wide temperature resilience - targeting reliability-critical digital interface and timing subsystems.

FAQ

What is the minimum external timing capacitor value supported by the 74HCT423D,118?

The 74HCT423D,118 does not specify a minimum C_EXT value; however, for stable operation with C_EXT < 50 pF, a power-up reset pulse is recommended per Figure 14 in the datasheet. Typical designs use ≥100 pF to minimize sensitivity to stray capacitance and ensure predictable t_W scaling with R_EXT. The 74HCT423D,118's inherent pin capacitance at nREXT/CEXT is 7 pF.

Can the 74HCT423D,118 be used with a 3.3 V supply?

No - the 74HCT423D,118 is specified only for 4.5 V to 5.5 V operation. Its TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max at V_CC = 5 V) and internal design require 5 V nominal supply. For 3.3 V systems, consider the 74LVC423 or SN74LV423, which are explicitly characterized down to 2 V.

How does retriggering affect the output pulse width of the 74HCT423D,118?

Each valid nA or nB edge occurring before the initial t_W expires resets the internal timer, extending the output pulse by another full t_W period. The 74HCT423D,118's retrigger time (t_rtrig) is 110 ns (typ.) at V_CC = 5 V with R_EXT = 5 kΩ and C_EXT = 0 pF - meaning successive triggers must be spaced ≥110 ns apart to guarantee extension. This enables duty cycles up to 100 %.

Is the 74HCT423D,118 pin-compatible with the 74HC423D?

Yes - the 74HCT423D,118 and 74HC423D share identical pinout, package (SO16/SOT109-1), and functional block diagram. The key difference is input threshold compatibility: 74HCT423D,118 accepts TTL-level inputs (VIH ≥ 2.0 V), while 74HC423D requires CMOS-level inputs (VIH ≥ 3.15 V at V_CC = 4.5 V). Both drive the same output levels and support identical R_EXT/C_EXT configurations.

What is the maximum recommended value for R_EXT in the 74HCT423D,118 timing network?

The 74HCT423D,118 specifies R_EXT up to 1000 kΩ at V_CC = 5.0 V. Beyond this, leakage currents and noise susceptibility increase significantly, potentially causing erratic timing or failure to trigger. For stable operation above 100 kΩ, use metal-film resistors and shielded layout; values >500 kΩ should include guard traces and local decoupling to maintain accuracy within ±10 % over temperature.