NXP Semiconductors 74HC221D,652

Overview

74HC221D,652 from Nexperia is a dual non-retriggerable monostable multivibrator in SO16 package, featuring independent negative-edge (nA) and positive-edge (nB) trigger inputs per channel, active-low reset (nRD), and complementary outputs (nQ/nQ). It delivers ±2% pulse width match between channels, 0.7×CEXT×REXT timing accuracy, and operates across 2–6 V supply with <5% pulse width variance. Used in debounce circuits, timing control, and pulse shaping in industrial logic systems.

For engineers reviewing the 74HC221D,652 datasheet, 74HC221D,652 pinout, 74HC221D,652 application, or 74HC221D,652 equivalent, key selection factors include non-retriggerable behavior, Schmitt-trigger nB inputs for slow-edge immunity, external R/C timing flexibility (REXT = 2–1000 kΩ, CEXT unrestricted), and guaranteed pulse stability over temperature and VCC.

Technical Context

The 74HC221D,652 implements two independent monostable circuits with internal compensation ensuring output pulse width (tW = 0.7 × CEXT × REXT) is virtually independent of VCC and temperature. Each channel accepts either falling-edge (nA) or rising-edge (nB) triggers, with hysteresis on nB inputs enabling jitter-free operation from slow-rising signals.

Reset is asynchronous and overriding: asserting nRD LOW terminates ongoing output pulses immediately. Outputs are complementary (nQ active LOW, nQ active HIGH), and timing components connect externally to dedicated pins (1REXT/CEXT, 2REXT/CEXT, 1CEXT, 2CEXT), with recommended grounding of unused CEXT pins to GND.

Key Specifications

Pinout & Package

74HC221D,652 is housed in a 16-pin SO (Small Outline) package with 1.27 mm pitch, JEDEC MS-012AC compliant, body width 3.9 mm, and moisture sensitivity level (MSL) 1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HCT221D,653 and SN74LV221ADBR, the 74HC221D,652 provides the widest supply range (2–6 V) and direct pin compatibility with 74LS123, making it the preferred choice for retrofitting older systems while supporting modern low-power operation - without requiring layout changes or voltage translation.

Availability

74HC221D,652 is available at Aetrix Electronics and suitable for industrial automation, embedded control, and legacy system upgrades requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for 74HC221D,652 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 discrete, logic, and power MOSFET solutions for automotive, industrial, and computing markets.

The 74HC221D,652 belongs to Nexperia's 74HC logic family - engineered for pin-compatible upgrades of legacy TTL systems while delivering lower power, wider voltage operation, and enhanced noise immunity in industrial environments.

FAQ

What is the maximum timing capacitor value supported by the 74HC221D,652?

The 74HC221D,652 datasheet specifies "no limits" for CEXT, meaning it supports any practical capacitance value - from picofarads to microfarads - as long as leakage and ESR remain within acceptable bounds. Pulse width scales linearly with CEXT (tW = 0.7 × CEXT × REXT), so large capacitors enable second-scale timing. However, large CEXT values require damping diodes during power-down to prevent damage from stored charge discharge through protection diodes.

Can the 74HC221D,652 be used in retriggerable mode?

No, the 74HC221D,652 is explicitly a non-retriggerable monostable - once triggered, further input transitions on nA or nB are ignored until the current output pulse completes. Retriggerable behavior is not supported by its internal architecture. For retriggerable operation, designers must select alternatives like the 74HC4538 or implement external logic; the 74HC221D,652's non-retriggerable nature ensures predictable, fixed-duration pulses essential for safety-critical timing.

How does the 74HC221D,652 handle simultaneous trigger and reset assertions?

When both trigger (nA or nB) and reset (nRD) are asserted simultaneously, the 74HC221D,652 prioritizes reset: nRD is asynchronous and overriding, forcing nQ LOW and nQ HIGH immediately, regardless of trigger state. This behavior is confirmed in the function table - an active LOW nRD always produces L/H outputs, even if nA/nB transitions occur concurrently. The device resumes normal operation only after nRD returns HIGH and a valid trigger edge is detected.

Is the 74HC221D,652 compatible with 3.3 V microcontroller GPIOs?

Yes, the 74HC221D,652 operates reliably from 2.0 V to 6.0 V, and its HC-series input thresholds scale with VCC (VIH ≈ 0.7×VCC, VIL ≈ 0.3×VCC). At VCC = 3.3 V, it accepts 3.3 V GPIO outputs directly - no level shifting required. Its outputs swing rail-to-rail, providing full 3.3 V logic levels compatible with downstream 74HC or ARM GPIO inputs, making the 74HC221D,652 ideal for mixed-voltage embedded timing applications.

Why must pins 6 and 14 (1CEXT, 2CEXT) be grounded if unused?

Pins 6 and 14 are dedicated external capacitor terminals for timing networks. If left floating, they introduce parasitic capacitance and noise susceptibility, degrading pulse width accuracy and potentially causing erratic triggering. The datasheet explicitly recommends grounding them to GND (pin 8) to stabilize bias conditions and prevent unintended coupling. This grounding ensures predictable RC timing behavior and avoids metastability in the internal timing comparator circuitry of the 74HC221D,652.