SCLS450H December   1999  – January 2025 SN74LV221A

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 = 2.5V ± 0.2V
    7. 4.7  Timing Requirements, VCC = 3.3V ± 0.3V
    8. 4.8  Timing Requirements, VCC = 5V ± 0.5V
    9. 4.9  Switching Characteristics, VCC = 2.5V ± 0.2V
    10. 4.10 Switching Characteristics, VCC = 3.3V ± 0.3V
    11. 4.11 Switching Characteristics, VCC = 5V ± 0.5V
    12. 4.12 Operating Characteristics
    13. 4.13 Input/Output Timing Diagram
  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. 7.1 Application Information
      1. 7.1.1 Caution in Use
      2. 7.1.2 Power-down Considerations
      3. 7.1.3 Output Pulse Duration
    2. 7.2 Power Supply Recommendations
    3. 7.3 Layout
      1. 7.3.1 Layout Guidelines
      2. 7.3.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      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

7.1.2 Power-down Considerations

Large values of Cext can cause problems when powering down the ’LV221A because of the amount of energy stored in the capacitor. When a system containing this device is powered down, the capacitor can discharge from VCC through the protection diodes at pin 2 or pin 14. Current through the input protection diodes must be limited to 30 mA; therefore, the turn-off time of the VCC power supply must not be faster than t = VCC × Cext/30 mA. For example, if VCC = 5 V and Cext = 15 pF, the VCC supply must turn off no faster than t = (5 V) × (15 pF)/30 mA = 2.5 ns. Usually, this is not a problem because power supplies are heavily filtered and cannot discharge at this rate. When a more rapid decrease of VCC to zero occurs, the ’LV221A can sustain damage. To avoid this possibility, use external clamping diodes.