SLVA720A July   2015  – October 2020 CD14538B , CD14538B-MIL , CD4047B , CD4047B-MIL , CD4098B , CD4098B-MIL , CD54HC123 , CD54HC221 , CD54HC4538 , CD54HCT123 , CD54HCT4538 , CD74HC123 , CD74HC221 , CD74HC423 , CD74HC4538 , CD74HC4538-Q1 , CD74HCT123 , CD74HCT221 , CD74HCT423 , CD74HCT4538 , SN54121 , SN54123 , SN54221 , SN54AHC123A , SN54AHCT123A , SN54LS123 , SN54LS123-SP , SN54LS221 , SN74121 , SN74221 , SN74AHC123A , SN74AHC123A-EP , SN74AHCT123A , SN74LS122 , SN74LS123 , SN74LS221 , SN74LS423 , SN74LV123A , SN74LV123A-EP , SN74LV123A-Q1 , SN74LV221A , SN74LV221A-Q1 , SN74LVC1G123

 

  1. 1Introduction
  2. 2Terminology
  3. 3Theory of Operation
    1. 3.1 Basic Concept
    2. 3.2 Operation
  4. 4Applications
    1. 4.1 General Design Considerations
      1. 4.1.1 Pulse Length Determination
        1. 4.1.1.1 Temperature Stability
    2. 4.2 SN74LVC1G123 Applications
      1. 4.2.1 Switch Debounce
        1. 4.2.1.1 Requirements
        2. 4.2.1.2 Schematic
        3. 4.2.1.3 Component Selection
      2. 4.2.2 Leading and Trailing Edge Detector
        1. 4.2.2.1 Requirements
        2. 4.2.2.2 Schematic
        3. 4.2.2.3 Component Selection
  5. 5Frequently Asked Questions
    1. 5.1 How do I calculate the output pulse length?
    2. 5.2 How do I configure the SN74LVC1G123's inputs for ______ edge triggering?
    3. 5.3 How stable is the output pulse length over VCC changes?
    4. 5.4 How stable is the output pulse length over temperature changes?
    5. 5.5 Which inputs of the SN74LVC1G123 have Schmitt-triggers?
    6. 5.6 Can I connect the Cext pin to ground?
  6. 6Revision History

4.2.1 Switch Debounce

When a human presses a button on a computer system, there is always the chance that the button press will be read incorrectly by the system. Most physical switches 'bounce' internally when pressed and can produce a large number of triggers to a computer system when the user only intended one. A system that changes multiple triggers into a single pulse is desirable in this situation.

The retriggerable functionality of the SN74LVC1G123 makes it an ideal choice for switch debouncing applications. By selecting a pulse length longer than the bounce length but shorter than a human would notice, the monostable multivibrator will change an unpredictable button press from a human into a predictable pulse of a selected width.