SCHS231E November   1998  – August 2024 CD54AC74 , CD74AC74

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Description
  4. 3 Pin Configuration and Functions
  5. 4 Specifications
    1. 4.1  Absolute Maximum Ratings
    2. 4.2  ESD Ratings
    3. 4.3  Recommended Operating Conditions
    4. 4.4  Thermal Information
    5. 4.5  Electrical Characteristics
    6. 4.6  Timing Requirements, VCC = 1.5 V
    7. 4.7  Timing Requirements, VCC = 3.3 V ± 0.3 V
    8. 4.8  Timing Requirements, VCC = 5 V ± 0.5 V
    9. 4.9  Switching Characteristics, VCC = 1.5 V
    10. 4.10 Switching Characteristics, VCC = 3.3 V ± 0.3 V
    11. 4.11 Switching Characteristics, VCC = 5 V ± 0.5 V
    12. 4.12 Operating Characteristics
  6. 5 Parameter Measurement Information
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Device Functional Modes
  8. 7 Application and Implementation
    1.     Power Supply Recommendations
    2. 7.1 Layout
      1. 7.1.1 Layout Guidelines
      2. 7.1.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support (Analog)
      1. 8.1.1 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.1.1 Layout Guidelines

Inputs must not float when using multiple bit logic devices. In many cases, functions or parts of functions of digital logic devices are unused. Some examples include situations when only two inputs of a triple-input AND gate are used, or when only 3 of the 4-buffer gates are used. Such input pins must not be left unconnected because the undefined voltages at the outside connections result in undefined operational states.

Specified in Layout Example for the CD74AC74 are rules that must be observed under all circumstances. All unused inputs of digital logic devices must be connected to a high or low bias to prevent them from floating. The logic level that must be applied to any particular unused input depends on the function of the device. Generally, they are tied to GND or VCC, whichever makes more sense or is more convenient.