MM74HC221AM

Overview

The MM74HC221AM is a dual non-retriggerable monostable multivibrator utilizing advanced silicon-gate CMOS technology. It operates within a supply voltage range of 2V to 6V and features Schmitt trigger inputs for noise immunity. The device generates a single output pulse upon triggering, with pulse width determined by external resistor and capacitor values using the formula PW = REXT × CEXT. It includes separate negative (A) and positive (B) transition triggered inputs, both of which can function as inhibit inputs, alongside a clear input for resetting the timing cycle.

Feature Summary

• Dual independent non-retriggerable monostable multivibrators in a single package
• Schmitt trigger A and B inputs enable infinite signal input rise or fall times
• Simple pulse width determination via external RC components
• Outputs protected from static discharge damage via diodes to VCC and ground

Applications

• Timing generation circuits requiring precise pulse widths
• Debouncing switches or mechanical contacts
• Pulse widening or narrowing applications
• Delay line implementations in digital logic systems

Procurement Notes

Verify the specific ordering suffix to confirm the package type, as the MM74HC221A series is available in multiple configurations including SOIC, SOP, and PDIP. Ensure the selected variant matches the required pinout and physical dimensions for the target PCB layout. Confirm that the manufacturer designation aligns with current corporate structures following industry acquisitions, as datasheets may retain legacy branding while representing updated production sources.

Selection Notes

Select this component when dual isolated timing channels are required within a single footprint. The CMOS technology offers low quiescent current consumption compared to TTL equivalents, making it suitable for battery-powered or power-sensitive designs. Verify that the external timing components meet the minimum resistance requirements relative to the supply voltage to ensure proper operation. Consider the propagation delay characteristics if strict timing synchronization with other system clocks is necessary.

Part Context

This device belongs to the 74HC family of high-speed CMOS logic devices, originally introduced by Fairchild Semiconductor. The MM74HC221A specifically provides two identical monostable circuits, allowing for compact design solutions where space is constrained. It serves as a functional equivalent to older bipolar transistor-based one-shots but with improved power efficiency and noise margins characteristic of modern CMOS processes.

Replacement Considerations

Check for direct pin-compatible alternatives from other manufacturers that specify dual non-retriggerable monostable functionality with HC logic levels. Ensure any substitute maintains the same Schmitt trigger input characteristics and supply voltage range. Verify that the replacement part supports the required output drive capability and propagation delays for the specific application timing constraints.