STMicroelectronics M74HC221B1R

Overview

M74HC221B1R from STMicroelectronics is a dual high-speed CMOS monostable multivibrator in 16-pin DIP package, featuring two independent retriggerable one-shots with negative-edge (A) and positive-edge (B) trigger inputs, active-low/active-high complementary outputs (Q/Q̄), and external RC timing control (t_WOUT = 150 ns to 60 s at V_CC = 4.5 V). It operates across 2–6 V, delivers 24 ns typical propagation delay at 6 V, and supports industrial temperature range (−55°C to +125°C) for timing-critical digital systems.

For engineers reviewing the M74HC221B1R datasheet, M74HC221B1R pinout, M74HC221B1R application, or M74HC221B1R equivalent, key selection criteria include retriggerable monostable behavior, dual independent timing channels, Schmitt-triggered CLR input, symmetrical output drive (±4 mA), and wide V_CC tolerance-critical for legacy TTL-compatible logic upgrades and pulse shaping in mixed-voltage control circuits.

Technical Context

The M74HC221B1R implements two independent monostable circuits using silicon gate C2MOS technology, each with dual-edge triggering (A: falling edge; B: rising edge) and Schmitt-triggered CLR for noise-immune reset. Timing is set externally via R_X/C_X networks, with K ≈ 0.7 yielding t_WOUT = 0.7·R_X·C_X.

Each channel features complementary Q/Q̄ outputs, balanced t_PLH/t_PHL delays (≤5% skew), and internal comparators with V_REFH/V_REFL thresholds derived from V_CC. Standby ICC ≤ 4 µA enables low-power timing hold states, while active ICC ≤ 700 µA at 5 V supports burst-mode operation.

Key Specifications

Pinout & Package

Package: Plastic DIP-16 (0.300" width), 16-pin through-hole, JEDEC MS-001AC compliant, lead finish matte tin.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV221A, M74HC221B1R offers superior noise immunity and broader voltage flexibility but trades off speed; versus CD74HC221E, it shares full functional equivalence but differs in manufacturing origin and traceability-critical for defense/aerospace BOM compliance.

Availability

M74HC221B1R is available at Aetrix Electronics and suitable for industrial motor control, automotive power sequencing, and medical equipment safety timers requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for M74HC221B1R 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing microcontrollers, analog ICs, power management devices, and discrete components for industrial, automotive, and consumer markets.

The M74HC221B1R belongs to ST's legacy HC logic family-engineered for pin- and function-compatibility with industry-standard 74-series logic while delivering enhanced speed, noise immunity, and power efficiency for retrofits and new designs.

FAQ

What is the minimum external capacitor value supported for reliable timing?

The M74HC221B1R requires C_X ≥ 100 pF for stable operation, as specified in the Recommended Operating Conditions table. Capacitors below this threshold cause excessive timing error due to internal node capacitance dominance and increased sensitivity to PCB stray capacitance. Ceramic C0G/NP0 types are recommended for <1% drift over temperature.

Can the device generate asymmetric output pulses?

No-the M74HC221B1R produces symmetric, fixed-width pulses determined solely by R_X·C_X (t_WOUT ≈ 0.7·R_X·C_X). Pulse width cannot be varied mid-cycle or independently adjusted for rising/falling edges. For asymmetric timing, external gating or cascaded monostables are required.

How does the retriggerable feature behave during an active monostable period?

When a new trigger occurs during the active monostable period, the output pulse width extends by a full t_WOUT interval from the trigger edge-not from the original expiration time. This "retrigger-and-extend" behavior is inherent to the internal comparator and flip-flop architecture, enabling dynamic timeout adjustment in real time.

Is the CLR input truly asynchronous, or does it require setup/hold timing?

The CLR input is asynchronous and Schmitt-triggered, meaning it requires no relationship to A/B timing edges or internal clocks. However, data sheet AC characteristics specify a minimum CLR pulse width (13 ns at V_CC = 6 V) to ensure reliable reset; shorter pulses may fail to clear the internal flip-flop state.