SLUSF78A June   2023  – November 2024 UCC28731-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
    1.     Pin Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Timing Requirements
    7. 5.7 Switching Characteristics
    8. 5.8 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Detailed Pin Description
        1. 6.3.1.1 VDD (Device Bias Voltage Supply)
        2. 6.3.1.2 GND (Ground)
        3. 6.3.1.3 HV (High Voltage Startup)
        4. 6.3.1.4 DRV (Gate Drive)
        5. 6.3.1.5 CBC (Cable Compensation)
        6. 6.3.1.6 VS (Voltage Sense)
        7. 6.3.1.7 CS (Current Sense)
      2. 6.3.2 Primary-Side Regulation (PSR)
      3. 6.3.3 Primary-Side Constant Voltage Regulation
      4. 6.3.4 Primary-Side Constant Current Regulation
      5. 6.3.5 Valley-Switching and Valley-Skipping
      6. 6.3.6 Startup Operation
      7. 6.3.7 Fault Protection
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Input Bulk Capacitance and Minimum Bulk Voltage
        2. 7.2.2.2 Transformer Turns Ratio, Inductance, Primary-Peak Current
        3. 7.2.2.3 Transformer Parameter Verification
        4. 7.2.2.4 Output Capacitance
        5. 7.2.2.5 VDD Capacitance, CVDD
        6. 7.2.2.6 VS Resistor Divider, Line Compensation, and Cable Compensation
      3. 7.2.3 Application Curves
    3. 7.3 Do's and Don'ts
    4. 7.4 Power Supply Recommendations
    5. 7.5 Layout
      1. 7.5.1 Layout Guidelines
      2. 7.5.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Device Nomenclature
        1. 8.1.1.1  Capacitance Terms in Farads
        2. 8.1.1.2  Duty-Cycle Terms
        3. 8.1.1.3  Frequency Terms in Hertz
        4. 8.1.1.4  Current Terms in Amperes
        5. 8.1.1.5  Current and Voltage Scaling Terms
        6. 8.1.1.6  Transformer Terms
        7. 8.1.1.7  Power Terms in Watts
        8. 8.1.1.8  Resistance Terms in Ω
        9. 8.1.1.9  Timing Terms in Seconds
        10. 8.1.1.10 DC Voltage Terms in Volts
        11. 8.1.1.11 AC Voltage Terms in Volts
        12. 8.1.1.12 Efficiency Terms
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

6.3.1.3 HV (High Voltage Startup)

The HV pin connects directly to the bulk capacitor to provide startup current to the VDD capacitor. The typical startup current is approximately 250µA which provides fast charging of the VDD capacitor. The internal HV startup device is active until VVDD exceeds the turn-on UVLO threshold of 21V at which time the HV startup device turns off. In the off state the HV leakage current is very low to minimize stand-by losses of the controller. When VVDD falls below the 7.7V UVLO turn-off threshold the HV startup device turns on.