NXP Semiconductors 74HCT423DB,118

Overview

74HCT423DB,118 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 Schmitt-trigger inputs on A/B trigger pins, supports external REXT/CEXT timing (2 kΩ–1000 kΩ / no capacitor limit), delivers propagation delays as low as 22 ns at VCC = 4.5 V, and operates across −40 °C to +125 °C for industrial control and power sequencing applications.

For engineers reviewing the 74HCT423DB,118 datasheet, 74HCT423DB,118 pinout, 74HCT423DB,118 application, or 74HCT423DB,118 equivalent, this device is critical for designs requiring adjustable, retriggerable timing pulses with direct reset control, high noise immunity on slow-rising inputs, and guaranteed TTL-level compatibility without level-shifting.

Technical Context

The 74HCT423DB,118 implements two independent monostable circuits, each with dual-edge triggering (nA: negative edge, nB: positive edge) and active-low synchronous reset (nRD). Pulse width is set by external REXT and CEXT components, and can be extended indefinitely via retriggering before timeout - enabling 0 % to 100 % duty-cycle flexibility. The device uses silicon-gate CMOS technology with TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max at VCC = 4.5–5.5 V).

Its Schmitt-trigger action on nA/nB inputs ensures robust operation with slow or noisy signals (input hysteresis ≥ 0.8 V typical), while the reset path provides deterministic termination of output pulses. Unlike the 74HCT123, it cannot be triggered via the reset input - confirming strict separation of reset and trigger functionality per channel.

Key Specifications

Pinout & Package

74HCT423DB,118 is housed in a plastic shrink small outline package (SSOP16) with 16 leads, body width 5.3 mm (SOT338-1), optimized for high-density PCB layouts and automated assembly.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HCT123D,653 and SN74LV123ADR, the 74HCT423DB,118 uniquely combines retriggerability, Schmitt-triggered inputs, and TTL-compatible thresholds in a single SSOP16 package - making it the only option for noise-immune, extendable pulse generation in 5 V industrial systems.

Availability

74HCT423DB,118 is available at Aetrix Electronics and suitable for industrial motor control, automotive power sequencing, and precision data acquisition requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for 74HCT423DB,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 specializing in secure connectivity solutions for automotive, industrial, and IoT applications, with leadership in high-reliability logic and interface ICs.

The 74HCT423DB,118 belongs to NXP's 74HCT logic family - engineered for robust 5 V TTL interoperability, wide temperature operation, and noise-tolerant timing in mission-critical embedded systems.

FAQ

What is the minimum pulse width achievable with 74HCT423DB,118?

The minimum pulse width of the 74HCT423DB,118 is approximately 75 ns when REXT = 5 kΩ and CEXT = 0 pF at VCC = 5.0 V. This value is confirmed in Table 7 of the datasheet under dynamic characteristics. For longer pulses, external REXT and CEXT values determine width via tW ≈ 0.45 × REXT × CEXT (with REXT in kΩ and CEXT in nF). The 74HCT423DB,118 does not support sub-75 ns pulses without external acceleration techniques.

Can 74HCT423DB,118 be used with 3.3 V logic systems?

No - the 74HCT423DB,118 is specified only for VCC = 4.5 V to 5.5 V and has TTL-compatible input thresholds (VIH ≥ 2.0 V, VIL ≤ 0.8 V). Applying 3.3 V violates the recommended operating conditions and risks unreliable triggering or increased static current. For 3.3 V systems, consider SN74LV123ADR instead, but note its lack of Schmitt-trigger inputs and retriggerability.

How does the retrigger function work on 74HCT423DB,118?

Retriggering on the 74HCT423DB,118 extends the current output pulse each time a valid edge arrives at nA (falling) or nB (rising), provided it occurs before the original timeout expires. The retrigger time trtrig is 110 ns (typical) at VCC = 5.0 V with REXT = 5 kΩ and CEXT = 0 pF. This allows indefinite pulse extension - critical for applications like motor ramping or gated data capture where duration depends on real-time events.

Is 74HCT423DB,118 pin-compatible with 74HC423DB variants?

Yes - the 74HCT423DB,118 shares identical pinout, package (SSOP16/SOT338-1), and functional diagram with 74HC423DB variants. However, electrical differences exist: 74HCT423DB,118 uses TTL-compatible input thresholds (VIH = 2.0 V min), while 74HC423DB requires CMOS thresholds (VIH = 3.15 V min at VCC = 4.5 V). Interchangeability requires verification of source logic family voltage levels.

What is the purpose of the 1CEXT and 2CEXT pins on 74HCT423DB,118?

Pins 6 and 14 (1CEXT, 2CEXT) connect the external timing capacitors to ground. Per Section 12.1.1 and Figure 13 of the datasheet, these pins must be externally tied to GND (pin 8) - not left floating - to ensure stable timing and minimize noise coupling into the RC network. Failure to ground them increases timing uncertainty and may cause erratic pulse widths or spurious outputs.