Nexperia USA Inc. 74HCT221D,118

Overview

74HCT221D,118 from Nexperia is a dual non-retriggerable monostable multivibrator in SO16 package, providing two independent edge-triggered timing channels with active-LOW reset. It operates from 4.5 V to 5.5 V, delivers pulse widths defined by t_W = 0.7 × C_EXTR_EXT, and features Schmitt-trigger inputs on nB pins for jitter-free triggering from slow-rising signals - used in digital debounce, pulse shaping, and timing control in industrial control logic.

For engineers reviewing the 74HCT221D,118 datasheet, 74HCT221D,118 pinout, 74HCT221D,118 application, or 74HCT221D,118 equivalent, key selection criteria include TTL-compatible input thresholds (VIH = 2.0 V min), non-retriggerable behavior, ±5% typical pulse width variance, reset propagation delay ≤77 ns at 4.5 V, and SO16 thermal derating above 110 °C.

Technical Context

The 74HCT221D implements two independent CMOS monostable circuits, each with separate negative-edge (nA) and positive-edge (nB) trigger inputs, plus direct active-LOW reset (nRD). Its non-retriggerable architecture ensures output pulses are immune to further input transitions once triggered - critical for stable one-shot timing in noisy environments.

Timing is externally programmable via R_EXT (2–1000 kΩ) and C_EXT (no upper limit), with internal compensation delivering pulse width stability virtually independent of V_CC and temperature. Schmitt-trigger action on all nB inputs provides hysteresis (typ. 0.4 V), enabling robust operation with slow or noisy input edges.

Key Specifications

Pinout & Package

74HCT221D,118 is housed in a plastic small outline package (SO16), SOT109-1, with 16 leads, 3.9 mm body width, and standard 1.27 mm lead pitch - compatible with automated surface-mount assembly and IPC-7351B footprints.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HC221D,653 and SN74LV221ADBR, the 74HCT221D,118 uniquely combines TTL-level compatibility, Schmitt-trigger noise immunity, and ±5% pulse width stability across full industrial temperature - making it optimal for legacy 5 V designs requiring robust, deterministic timing.

Availability

74HCT221D,118 is available at Aetrix Electronics and suitable for industrial HMI debounce, motor control timeout supervision, serial communication glitch filtering, and digital edge detection requiring stable component supply across extended temperature ranges.

Supply support for 74HCT221D,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

Nexperia is a global semiconductor expert focused on high-volume, high-reliability logic, discrete, and MOSFET solutions - serving automotive, industrial, and consumer markets with ISO/TS 16949-certified manufacturing.

The 74HCT221D belongs to Nexperia's 74HCT logic family, engineered specifically for TTL-compatible interfacing in industrial control systems where noise immunity, timing predictability, and extended temperature operation are mandatory.

FAQ

What is the minimum external timing resistor value supported by the 74HCT221D,118?

The datasheet specifies R_EXT down to 2 kΩ at V_CC = 5.0 V. Using lower values risks exceeding the maximum output current rating (±25 mA) during timing node discharge and may cause pulse width compression or timing inaccuracy due to internal node loading effects.

Can the 74HCT221D,118 operate reliably with C_EXT > 1 μF?

Yes - the datasheet states "no limits" for C_EXT value. However, large capacitors (e.g., >100 nF) require external damping diodes (germanium or Schottky) during power-down to prevent reverse current through input protection diodes, as detailed in Figure 16 of the datasheet.

Is the 74HCT221D,118 pin-compatible with the 74LS221?

No - although both are dual monostables, the 74LS221 uses a different pinout (e.g., reset on pin 1, not pin 3), lacks Schmitt-trigger inputs, and has TTL-compatible but non-identical timing characteristics. Direct replacement requires PCB redesign and timing validation.

Does the 74HCT221D,118 support retriggering during an active output pulse?

No - it is explicitly a non-retriggerable monostable. Once triggered, further transitions on nA or nB inputs are ignored until the output pulse completes or is terminated by nRD. This behavior is confirmed in Table 3 (Function table) and Section 6 of the datasheet.