NXP Semiconductors 74HCT221DB,112

Overview

74HCT221DB,112 from Nexperia is a dual non-retriggerable monostable multivibrator with independent reset inputs, designed for precise pulse generation and timing control in digital logic systems. It features two identical monostable circuits, each with negative-edge (nA) and positive-edge (nB) trigger inputs, active-low reset (nRD), complementary outputs (nQ/nQ), and external REXT/CEXT timing control. Typical output pulse width stability is ±5%, with propagation delays as low as 21 ns at VCC = 4.5 V - used in debounce circuits, clock stretching, and event timing in industrial control modules.

For engineers reviewing the 74HCT221DB,112 datasheet, 74HCT221DB,112 pinout, 74HCT221DB,112 application, or 74HCT221DB,112 equivalent, key selection criteria include non-retriggerable behavior, Schmitt-trigger nB inputs for noise immunity, reset override capability, HCT-level TTL-compatible input thresholds, and SO16 package compatibility with legacy 74-series layouts.

Technical Context

The 74HCT221DB,112 implements two independent monostable multivibrators using high-speed Si-gate CMOS technology compliant with JEDEC 7A. Each circuit triggers on either nA (LOW-going) or nB (HIGH-going), with internal compensation ensuring pulse width independence from VCC and temperature variation.

Timing is set externally via REXT and CEXT pins (pins 7, 15, 6, 14); output pulse width follows tW = 0.7 × REXT × CEXT. The nB inputs include hysteresis for jitter-free triggering from slow-rising signals, and nRD provides asynchronous, overriding reset that forces nQ LOW and nQ HIGH regardless of ongoing timing cycle.

Key Specifications

Pinout & Package

74HCT221DB,112 is housed in a 16-pin SO (Small Outline) package (SO16), 3.9 mm body width, 1.27 mm pitch, with gull-wing leads and moisture sensitivity level MSL3. Pin 8 is GND; pin 16 is VCC; pins 1/9, 2/10, 3/11, 4/12, 5/13, 6/14, 7/15 are functionally paired across both monostables.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HCT221DB,112, the 74HCT123DB,112 supports pulse retriggering but sacrifices noise immunity and exact pulse matching, while SN74LVC221APWR enables 3.3 V integration but removes critical hysteresis and alters timing behavior - neither offers pin-compatible or functionally identical replacement.

Availability

74HCT221DB,112 is available at Aetrix Electronics and suitable for industrial automation, automotive body control modules, and test equipment requiring stable component supply, long-term lifecycle support, and guaranteed traceability.

Supply support for 74HCT221DB,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

Nexperia is a global semiconductor leader specializing in high-volume, high-reliability discrete, logic, and power MOSFET solutions for automotive, industrial, and computing markets.

The 74HCT221DB,112 belongs to Nexperia's 74HCT logic family - engineered for robust 5 V TTL-compatible operation in harsh environments, with emphasis on timing precision, noise resilience, and long-term manufacturability.

FAQ

What is the maximum recommended value for REXT in the 74HCT221DB,112?

The datasheet specifies REXT up to 1000 kΩ at VCC = 5.0 V. Using higher values increases susceptibility to leakage current errors and temperature drift, degrading pulse width accuracy. For stable operation across −40 °C to +125 °C, Nexperia recommends staying within 2–100 kΩ with 1% metal-film resistors. The 74HCT221DB,112's internal timing network is optimized for this range to maintain ±5% pulse variance.

Can the 74HCT221DB,112 operate with a single shared timing capacitor for both monostables?

Yes - pins 6 (2CEXT) and 14 (1CEXT) can be shorted and connected to one CEXT, while pins 7 and 15 serve as separate REXT nodes. This configuration allows synchronized pulse widths with independent duration control. However, the 74HCT221DB,112 datasheet notes that grounding pins 6 and 14 externally to GND is recommended unless actively used, so shared-C use requires careful layout to avoid parasitic coupling.

Does the 74HCT221DB,112 support operation below 4.5 V?

No - the 74HCT221DB,112 is specified only for VCC = 4.5 V to 5.5 V. At 4.0 V, input thresholds fall outside HCT compliance (VIH min drops below 2.0 V), propagation delays increase unpredictably, and pulse width accuracy degrades beyond ±15%. For 3 V operation, Nexperia's 74LVC221A is the designated alternative, not the 74HCT221DB,112.

How does the nB input hysteresis improve noise immunity in the 74HCT221DB,112?

The nB inputs feature built-in Schmitt-trigger hysteresis with typical threshold separation of 0.8 V (e.g., 1.0 V low-to-high, 1.8 V high-to-low). This prevents multiple false triggers from slow-rising or noisy signals - such as those from long PCB traces or unshielded sensors - by requiring a full voltage swing across the hysteresis band before recognition. The 74HCT221DB,112 leverages this to enable reliable triggering without external RC filters in electrically noisy industrial settings.

Is the 74HCT221DB,112 pin-compatible with the original Philips 74HCT221DB?

Yes - the 74HCT221DB,112 is the direct successor to the Philips Semiconductors 74HCT221DB, retaining identical pinout, electrical specifications, and package dimensions. Following Nexperia's 2017 spin-off, all documentation, manufacturing, and quality control were transferred without change; the "112" suffix denotes the same SO16 package variant previously offered by Philips.