SGLS245E May   2020  – May 2020 UCC2813-0-Q1 , UCC2813-1-Q1 , UCC2813-2-Q1 , UCC2813-3-Q1 , UCC2813-4-Q1 , UCC2813-5-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Block Diagram
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Detailed Pin Descriptions
        1. 8.3.1.1 COMP
        2. 8.3.1.2 CS
        3. 8.3.1.3 FB
        4. 8.3.1.4 GND
        5. 8.3.1.5 OUT
        6. 8.3.1.6 RC
        7. 8.3.1.7 REF
        8. 8.3.1.8 VCC
      2. 8.3.2  Undervoltage Lockout (UVLO)
      3. 8.3.3  Self-Biasing, Active Low Output
      4. 8.3.4  Reference Voltage
      5. 8.3.5  Oscillator
      6. 8.3.6  Synchronization
      7. 8.3.7  PWM Generator
      8. 8.3.8  Minimum Off-Time Adjustment (Dead-Time Control)
      9. 8.3.9  Leading Edge Blanking
      10. 8.3.10 Minimum Pulse Width
      11. 8.3.11 Current Limiting
      12. 8.3.12 Overcurrent Protection and Full-Cycle Restart
      13. 8.3.13 Soft Start
      14. 8.3.14 Slope Compensation
    4. 8.4 Device Functional Modes
      1. 8.4.1 Normal Operation
      2. 8.4.2 UVLO Mode
      3. 8.4.3 Soft-Start Mode
      4. 8.4.4 Fault Mode
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1  Bulk Capacitor Calculation
        2. 9.2.2.2  Transformer Design
        3. 9.2.2.3  MOSFET and Output Diode Selection
        4. 9.2.2.4  Output Capacitor Calculation
        5. 9.2.2.5  Current Sensing Network
        6. 9.2.2.6  Gate Drive Resistor
        7. 9.2.2.7  REF Bypass Capacitor
        8. 9.2.2.8  RT and CT
        9. 9.2.2.9  Start-Up Circuit
        10. 9.2.2.10 Voltage Feedback Compensation Procedure
          1. 9.2.2.10.1 Power Stage Gain, Zeroes, and Poles
          2. 9.2.2.10.2 Compensating the Loop
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Related Links
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Community Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

パッケージ・オプション

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発注情報

8.3.11 Current Limiting

A 1-V (typical) cycle-by-cycle current limit threshold is incorporated into the UCC2813-x-Q1 family. The 100-ns leading-edge-blanking interval is applied to this current-limiting circuitry. The blanking overrides the current-limit comparator output to prevent the leading-edge switch noise from triggering a current-limit function. Propagation delay from the current-limit comparator to the output is typically 70 ns. This high-speed path minimizes power semiconductor dissipation during an overload by abbreviating the ON time.

For increased efficiency in the current-sense circuitry, the circuit shown in Figure 26 can be used. Resistors RA and RB bias the actual current-sense resistor voltage up, allowing a smaller current sense amplitude to be used. This circuitry provides current-limiting protection with lower power-loss current sensing.

UCC2813-0-Q1 UCC2813-1-Q1 UCC2813-2-Q1 UCC2813-3-Q1 UCC2813-4-Q1 UCC2813-5-Q1 u133_18.gifFigure 26. Biasing CS For Lower
Current-Sense Voltage
UCC2813-0-Q1 UCC2813-1-Q1 UCC2813-2-Q1 UCC2813-3-Q1 UCC2813-4-Q1 UCC2813-5-Q1 u133-19.gifFigure 27. CS Pin Voltage with Biasing

The example shown uses a 200-mV full-scale signal at the current sense resistor. Resistor RB biases this up by approximately 700 mV to match the 0.9-V minimum specification of the current-limit comparator of the IC. The value of resistor RA changes with the specific device used, due to the different reference voltages. The resistor values should be selected for minimal power loss. For example, a 50-µA bias current sets RB = 13 kΩ, and RA = 75 kΩ for UCC2813-[0,1,2,4]-Q1 or RA = 56 kΩ for UCC2813-[3,5]-Q1 devices.