NXP Semiconductors 74HCT423N,112

Overview

74HCT423N,112 from NXP Semiconductors is a dual retriggerable monostable multivibrator with independent reset inputs, designed for precise pulse generation and extension in TTL-compatible digital systems. It features two independent channels, Schmitt-trigger inputs on A/B trigger pins, 16-pin DIP package (SOT38-4), −40 °C to +125 °C operating range, and supports external REXT/CEXT timing control down to ~20 ns minimum pulse width at VCC = 4.5 V - used in debounce, timing synchronization, and programmable delay circuits.

For engineers reviewing the 74HCT423N,112 datasheet, 74HCT423N,112 pinout, 74HCT423N,112 application, or 74HCT423N,112 equivalent, this device delivers deterministic retriggerable output pulses with direct active-LOW reset, dual-edge triggering (nA: negative edge, nB: positive edge), and robust noise immunity via Schmitt-triggered inputs - critical for industrial control logic and legacy TTL system upgrades.

Technical Context

The 74HCT423N,112 implements two independent CMOS monostable multivibrators, each with gated retrigger capability via nA (active LOW-going) or nB (active HIGH-going) inputs. Pulse width is set by external REXT and CEXT components, with typical tW = 0.45 × REXT(kΩ) × CEXT(nF) for CEXT > 10 nF.

Reset is asynchronous and dominant: asserting nRD LOW forces nQ LOW, nQ HIGH, and blocks further triggering. Input thresholds are TTL-compatible (VIH = 2.0 V min, VIL = 0.8 V max at VCC = 4.5–5.5 V), and all inputs except nRD include Schmitt-trigger hysteresis for slow-slew signal tolerance.

Key Specifications

Pinout & Package

74HCT423N,112 uses the plastic dual in-line package SOT38-4 (16-pin DIP, 300 mil), with through-hole mounting and industry-standard pin spacing (2.54 mm). Pin 1 index located at top-left corner; body height ≈ 4.2 mm.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HCT123N,653 and SN74LV123AN, the 74HCT423N,112 uniquely combines retriggerable operation with Schmitt-triggered inputs and full TTL compatibility - making it the only option among the three that supports robust, noise-immune, arbitrarily extensible pulse generation in industrial 5 V systems.

Availability

74HCT423N,112 is available at Aetrix Electronics and suitable for industrial control panels, automotive body electronics, legacy system refurbishment, and test equipment requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for 74HCT423N,112 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 leader focused on secure connectivity solutions for automotive, industrial, and IoT applications, with deep expertise in logic, interface, and power management ICs.

The 74HCT423N,112 belongs to NXP's legacy HC/HCT logic family - engineered for reliable, pin-compatible upgrades of obsolete TTL components while delivering improved power efficiency, temperature resilience, and noise immunity.

FAQ

What is the minimum external timing capacitor value supported by the 74HCT423N,112?

The 74HCT423N,112 does not specify a minimum CEXT value; however, for stable operation with CEXT < 50 pF, a power-up reset pulse is recommended to prevent spurious output. The device's inherent pin capacitance at nREXT/CEXT pins is 7 pF, and design guidance assumes CEXT ≥ 10 pF for predictable pulse width using the tW = 0.45 × REXT × CEXT formula. Below 10 pF, propagation delay dominates timing behavior.

Can the 74HCT423N,112 generate asymmetric output waveforms?

Yes - the 74HCT423N,112 inherently produces complementary outputs (nQ and nQ) with matched rise/fall times (tt ≤ 22 ns at VCC = 4.5 V), enabling true differential or enable/disable signaling. Asymmetry can be introduced externally by loading nQ and nQ differently or adding passive RC networks, but the core device delivers symmetrical, rail-to-rail transitions without added components.

How does the 74HCT423N,112 handle simultaneous assertion of nA, nB, and nRD?

The 74HCT423N,112 gives absolute priority to nRD: when nRD is LOW, it forces nQ = LOW and nQ = HIGH regardless of nA or nB states and blocks all triggering. If nRD is HIGH and both nA (falling) and nB (rising) occur simultaneously, the internal logic resolves based on propagation delays - typically resulting in a single, well-defined output pulse determined by the faster path (nB → nQ tpd ≈ 22 ns vs. nA → nQ ≈ 26 ns at VCC = 4.5 V).

Is the 74HCT423N,112 compatible with 3.3 V logic systems?

No - the 74HCT423N,112 is specified only for VCC = 4.5 V to 5.5 V and has TTL-compatible input thresholds (VIH ≥ 2.0 V). While it may function at 3.3 V with marginal noise margin, NXP does not guarantee performance outside the rated supply range. For 3.3 V systems, consider the 74LVC123A or SN74LV123A, which are explicitly characterized at 3.3 V.

What is the maximum recommended value for REXT when using the 74HCT423N,112?

The datasheet specifies REXT ≤ 1000 kΩ at VCC = 5.0 V. Higher values increase sensitivity to leakage current and stray capacitance, degrading pulse width accuracy and stability. At REXT = 1 MΩ and CEXT = 100 nF, tW ≈ 45 ms (typ.), but variation exceeds ±20 % due to input bias current (≤172 μA per nA/nB pin) and dielectric absorption in large capacitors. For precision timing, REXT ≤ 100 kΩ is strongly recommended.