MM74HC123AN

Overview

The MM74HC123AN is a dual retriggerable monostable multivibrator manufactured by onsemi. It utilizes advanced silicon-gate CMOS technology to provide speeds comparable to low-power Schottky TTL while maintaining low power consumption and high noise immunity. The device features two independent circuits, each with negative (A) and positive (B) transition triggered inputs, as well as a clear input for resetting the output. It supports a wide power supply range of 2V to 6V and includes Schmitt trigger inputs to accommodate slow rise and fall times.

Feature Summary

• Retriggerable operation allows pulse extension when triggered repeatedly during the output pulse generation phase.
• Schmitt trigger inputs on both A and B channels enable reliable triggering even with slow signal transitions.
• Utilizes linear CMOS techniques to achieve stable pulse width performance across varying temperatures and supply voltages.
• Includes a dedicated clear input that resets the internal latch and forces the output to its quiescent state.

Applications

• Generating precise timing pulses in digital logic systems
• Debouncing mechanical switches to eliminate contact bounce signals
• Creating fixed-duration delays in sequential circuit designs

Procurement Notes

Verify the manufacturer origin, as this component was originally produced by Fairchild Semiconductor before acquisition by onsemi. Confirm the package type matches the required PCB footprint, specifically the 16-Lead Plastic Dual-In-Line Package (PDIP). Ensure the ordering code corresponds to the standard version without tape and reel suffixes if discrete components are needed.

Selection Notes

Select this component when a dual-channel monostable multivibrator with Schmitt trigger inputs is required. It is suitable for applications needing compatibility with LS-TTL loads due to its fanout capability. Consider the propagation delay specifications relative to the system clock speed. Verify that the external RC timing components can support the desired pulse width range within the operating voltage constraints.

Part Context

This part belongs to the 74HC series of high-speed CMOS logic devices. It is functionally compatible with the standard 74LS logic family regarding pinouts and basic operations. The 'N' suffix indicates the 16-lead PDIP package format. It serves as a fundamental building block for timing and waveform generation tasks in mixed-signal environments.

Replacement Considerations

Direct substitutes include other 74HC123 variants from different manufacturers such as Texas Instruments or Nexperia, provided they match the PDIP-16 package and electrical characteristics. Ensure any replacement maintains the retriggerable functionality and Schmitt trigger input requirements specified in the design.

FAQ

How does the retriggerable feature affect the output pulse width?

If a valid trigger occurs while the output is already HIGH, the output pulse width is extended from the moment of the new trigger until the full timing cycle completes based on the last trigger event.

What is the purpose of the Clear input?

The Clear input resets the one-shot circuit. When taken LOW, it forces the Q output to its quiescent LOW state and rapidly charges the external timing capacitor, effectively terminating the current pulse early.