SLUSEW0 December   2023 UCC28750

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Timing Requirements
    8. 6.8 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Detailed Pin Descriptions
      1. 7.3.1 VDD - Input Bias
      2. 7.3.2 DRV - Gate Drive Out
      3. 7.3.3 CS - Current Sensing
      4. 7.3.4 FB - Feedback
      5. 7.3.5 FLT - Fault
      6. 7.3.6 GND - Ground Return
    4. 7.4 Feature Description
      1. 7.4.1 Soft Start
      2. 7.4.2 Control Law
      3. 7.4.3 Frequency Dithering
      4. 7.4.4 Fault Protections
        1. 7.4.4.1 VDD Overvoltage and Undervoltage Lockout
        2. 7.4.4.2 Internal Overtemperature Protection
        3. 7.4.4.3 Output Overpower Protection
        4. 7.4.4.4 Output Short-Circuit Protection
        5. 7.4.4.5 FLT Pin Protections
      5. 7.4.5 Slope Compensation
    5. 7.5 Device Functional Modes
      1. 7.5.1 Off
      2. 7.5.2 Startup
      3. 7.5.3 On
      4. 7.5.4 Fault
      5. 7.5.5 Disabled
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Application
      2. 8.2.2 Design Requirements
      3. 8.2.3 Detailed Design Procedure
        1. 8.2.3.1 Input Bulk Capacitance with Minimum Bulk Voltage
        2. 8.2.3.2 Transformer Turns Ratio and Inductance
        3. 8.2.3.3 Current Sense and Slope Compensation Network
        4. 8.2.3.4 Output Capacitors
        5. 8.2.3.5 VDD Capacitance, CVDD
      4. 8.2.4 Application Performance Plots
        1. 8.2.4.1 Startup
        2. 8.2.4.2 Load Transients
        3. 8.2.4.3 Q1 Drain Voltage Evaluation
      5. 8.2.5 What to Do and What Not to Do
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

7.3.1 VDD - Input Bias

The VDD pin provides the bias to the controller, powering the internal references, regulators, and the undervoltage lockout (UVLO) circuit. The VDD pin is typically powered through a resistor network connected to the rectified bulk voltage and later an auxiliary winding in an AC/DC flyback application or a separate, active source outside of AC/DC applications. The VDD pin has a wide range of operation from a turn on of 15.3V, Vuvlo(on), to a turn off of 9V, Vuvlo(off), and a max voltage of 28V, Vovlo. The VDD pin has low startup current, decreasing startup time and lowering the power loss of the trickle charging network used in AC/DC flyback applications.

In addition to the CVDD capacitors shown in figures Figure 7-3 and Figure 7-4, bypass capacitors can be added for additional filtering at the pin.

GUID-20230918-SS0I-PKG5-JBPQ-CSF2MVBN2XFV-low.svg Figure 7-3 Biasing paths in a flyback application
GUID-20230918-SS0I-MHHV-08QN-9G3P9DKDHDQD-low.svg Figure 7-4 Biasing path using two diodes to split the VDD capacitance

Refer to Section 8.2.3.5 in the design guide to size the VDD pin capacitance.