NXP Semiconductors 74HC221D,653

Overview

74HC221D,653 from Nexperia is a dual non-retriggerable monostable multivibrator in SO16 package, featuring two independent edge-triggered timing channels with active-low reset, ±2% pulse width match between circuits, 0.7×CEXT×REXT output pulse width formula, and Schmitt-trigger inputs on nB pins for noise immunity. It is used in digital timing control, debounce circuits, and pulse shaping in industrial control panels.

For engineers reviewing the 74HC221D,653 datasheet, 74HC221D,653 pinout, 74HC221D,653 application, or 74HC221D,653 equivalent, key selection considerations include non-retriggerable behavior, external R/C timing flexibility (REXT = 2–1000 kΩ, CEXT unrestricted), propagation delays under 77 ns at 4.5 V, dual-edge trigger support (nA: negative-edge, nB: positive-edge), and reset override capability.

Technical Context

The 74HC221D,653 implements two independent monostable multivibrators using high-speed Si-gate CMOS technology compliant with JEDEC 7A. Each channel accepts either a falling edge on nA or rising edge on nB to initiate a single output pulse, with no retriggering during active output - ensuring deterministic timing in interrupt-driven systems.

Timing is set externally via REXT and CEXT pins; pulse width tW = 0.7 × CEXT × REXT is stable across VCC (2–6 V) and temperature (−40 to +125 °C), with typical variation <±5%. The overriding active-low nRD input forces immediate termination of ongoing pulses, enabling synchronous system reset.

Key Specifications

Pinout & Package

74HC221D,653 is housed in a 16-pin SOIC (Small Outline Integrated Circuit) package, 3.9 mm wide, with standard 1.27 mm pitch and gull-wing leads. Pin 8 is GND; Pin 16 is VCC; both outputs per channel are complementary (nQ active LOW, nQ active HIGH).

Key Features

Applications

Equivalent & Alternatives

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

Compared with 74HC221D,653, SN74LV221AIPWR offers lower supply voltage operation but sacrifices Schmitt-trigger noise immunity, while 74HCT221D,653 retains full functional equivalence with enhanced TTL input compatibility - making it ideal for brownfield 5 V system upgrades.

Availability

74HC221D,653 is available at Aetrix Electronics and suitable for industrial control panels, automotive body electronics, and consumer appliance timing circuits requiring stable component supply across extended temperature ranges and multi-year production cycles.

Supply support for 74HC221D,653 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 leader in discrete, logic, and PowerMOS semiconductors, spun off from NXP's Standard Products division in 2017 and focused on automotive, industrial, computing, and consumer markets.

The 74HC221D,653 belongs to Nexperia's 74HC logic family - designed for high-noise industrial environments requiring reliable, low-power, pin-compatible replacements for legacy TTL timing ICs.

FAQ

What is the function of the nB inputs on the 74HC221D,653?

The nB inputs (pins 2 and 10) on the 74HC221D,653 are positive-edge-triggered inputs with built-in Schmitt-trigger hysteresis. This design allows clean triggering from slow-rising or noisy signals such as mechanical switches or analog sensor outputs. Unlike nA inputs, nB does not require sharp edges - making the 74HC221D,653 especially robust in electrically harsh environments like factory floors or automotive cabins.

Can the 74HC221D,653 generate asymmetric pulse widths on its two channels?

Yes - the 74HC221D,653 supports independent timing per channel because each has dedicated REXT/CEXT nodes (pins 7/15 and 6/14). By selecting different resistor-capacitor combinations for channel 1 (1REXT/CEXT, 1CEXT) and channel 2 (2REXT/CEXT, 2CEXT), designers can configure distinct pulse widths - for example, 100 µs on channel 1 and 2 ms on channel 2 - without cross-talk or interaction between the monostables.

Is the 74HC221D,653 pin-compatible with the 74LS221?

No - the 74HC221D,653 is not pin-compatible with the 74LS221. It is pin-compatible with the 74LS123 and 74HC123, as confirmed in the datasheet's "Pin assignments for the '221' are identical to those of the '123'". The 74LS221 uses a different pinout and lacks the nB Schmitt inputs and matched pulse width specification found in the 74HC221D,653.

How does the reset input (nRD) affect ongoing output pulses in the 74HC221D,653?

The nRD input (pins 3 and 11) on the 74HC221D,653 is an asynchronous active-LOW override that immediately terminates any active output pulse on its associated channel. When nRD goes LOW, both nQ and nQ return to their quiescent states (nQ = HIGH, nQ = LOW) regardless of remaining timing period - enabling hard real-time abort functionality in safety interlocks or fault-clearing sequences.

What is the recommended practice for connecting CEXT pins on the 74HC221D,653?

The datasheet explicitly recommends grounding pins 6 (2CEXT) and 14 (1CEXT) externally to pin 8 (GND). This ensures stable reference for the internal timing comparator and prevents floating node instability that could cause erratic pulse width or false triggering. Failure to ground these pins may result in unpredictable timing behavior, especially under temperature variation or EMI exposure - a critical consideration in the 74HC221D,653's target applications.