SGLS245F May   2004  – April 2025 UCC2813-0-Q1 , UCC2813-1-Q1 , UCC2813-2-Q1 , UCC2813-3-Q1 , UCC2813-4-Q1 , UCC2813-5-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  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 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Detailed Pin Descriptions
        1. 7.3.1.1 COMP
        2. 7.3.1.2 CS
        3. 7.3.1.3 FB
        4. 7.3.1.4 GND
        5. 7.3.1.5 OUT
        6. 7.3.1.6 RC
        7. 7.3.1.7 REF
        8. 7.3.1.8 VCC
      2. 7.3.2  Undervoltage Lockout (UVLO)
      3. 7.3.3  Self-Biasing, Active Low Output
      4. 7.3.4  Reference Voltage
      5. 7.3.5  Oscillator
      6. 7.3.6  Synchronization
      7. 7.3.7  PWM Generator
      8. 7.3.8  Minimum Off-Time Adjustment (Dead-Time Control)
      9. 7.3.9  Leading Edge Blanking
      10. 7.3.10 Minimum Pulse Width
      11. 7.3.11 Current Limiting
      12. 7.3.12 Overcurrent Protection and Full-Cycle Restart
      13. 7.3.13 Soft Start
      14. 7.3.14 Slope Compensation
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal Operation
      2. 7.4.2 UVLO Mode
      3. 7.4.3 Soft-Start Mode
      4. 7.4.4 Fault Mode
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Bulk Capacitor Calculation
        2. 8.2.2.2  Transformer Design
        3. 8.2.2.3  MOSFET and Output Diode Selection
        4. 8.2.2.4  Output Capacitor Calculation
        5. 8.2.2.5  Current Sensing Network
        6. 8.2.2.6  Gate Drive Resistor
        7. 8.2.2.7  REF Bypass Capacitor
        8. 8.2.2.8  RT and CT
        9. 8.2.2.9  Start-Up Circuit
        10. 8.2.2.10 Voltage Feedback Compensation Procedure
          1. 8.2.2.10.1 Power Stage Gain, Zeroes, and Poles
          2. 8.2.2.10.2 Compensating the Loop
      3. 8.2.3 Application Curves
    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 Related Links
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • D|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.2.9 Start-Up Circuit

At start-up, the device gets its power directly from the high voltage bulk, through a high-voltage resistor RH. The selection of start-up resistor is the tradeoff between power loss and start-up time. The current flowing through RH at minimum input voltage must be higher than the VCC current under UVLO condition (0.2 mA at its maximum value). A 300-kΩ resistor is chosen as the result of the tradeoff.

After VCC is charged up above the UVLO turnon threshold, UCC2813-0-Q1 starts to operate and consumes full operating current. At the beginning, because the output voltage is low, VCC cannot get energy from the auxiliary winding. The VCC capacitor is required to hold enough energy to prevent its voltage drop below UVLO during the start-up time, until the output reaches high enough. A larger capacitor holds more energy but slows down the start-up time. In this design, a 120-µF capacitor is chosen to provide enough energy for the start-up purpose.