SLUSBL5A February   2015  – June 2019 UCC28730


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Zero-Power Input Consumption at No-Load
  4. Revision History
  5. Pin Configuration and Functions
    1.     Pin Functions
  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 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Detailed Pin Description
        1. VDD (Device Bias Voltage Supply)
        2. GND (Ground)
        3. HV (High Voltage Startup)
        4. DRV (Gate Drive)
        5. CBC (Cable Compensation)
        6. VS (Voltage Sense)
        7. CS (Current Sense)
      2. 7.3.2 Primary-Side Regulation (PSR)
      3. 7.3.3 Primary-Side Constant Voltage Regulation
      4. 7.3.4 Primary-Side Constant Current Regulation
      5. 7.3.5 Wake-Up Detection and Function
      6. 7.3.6 Valley-Switching and Valley-Skipping
      7. 7.3.7 Startup Operation
      8. 7.3.8 Fault Protection
    4. 7.4 Device Functional Modes
  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. Stand-By Power Estimate
        2. Input Bulk Capacitance and Minimum Bulk Voltage
        3. Transformer Turns Ratio, Inductance, Primary-Peak Current
        4. Transformer Parameter Verification
        5. Output Capacitance
        6. VDD Capacitance, CVDD
        7. VS Resistor Divider, Line Compensation, and Cable Compensation
        8. VS Wake-Up Detection
      3. 8.2.3 Application Curves
    3. 8.3 Do's and Don'ts
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
      2. 11.1.2 Device Nomenclature
        1.  Capacitance Terms in Farads
        2.  Duty-Cycle Terms
        3.  Frequency Terms in Hertz
        4.  Current Terms in Amperes
        5.  Current and Voltage Scaling Terms
        6.  Transformer Terms
        7.  Power Terms in Watts
        8.  Resistance Terms in Ω
        9.  Timing Terms in Seconds
        10. DC Voltage Terms in Volts
        11. AC Voltage Terms in Volts
        12. Efficiency Terms
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

VS Resistor Divider, Line Compensation, and Cable Compensation

The VS divider resistors determine the output voltage regulation point of the flyback converter. Also, the high-side divider resistor, RS1, determines the line voltage at which the controller enables continuous DRV operation. RS1 is initially determined based on the transformer primary to auxiliary turns ratio and the desired input voltage operating threshold.

Equation 27. UCC28730 qu26_lusbl5.gif

The low-side VS divider resistor, RS2, is selected based on the desired constant-voltage output regulation target, VOCV.

Equation 28. UCC28730 qu27_lusbl5.gif

The UCC28730 can maintain tight constant-current regulation over input line by utilizing the line compensation feature. The line compensation resistor value, RLC, is determined by various system parameters and the combined gate-drive turn-off and MOSFET turn-off delays, tD. Assume a 50-ns internal propagation delay in the UCC28730.

Equation 29. UCC28730 qu28_lusbl5.gif

The UCC28730 provides adjustable cable compensation of up to approximately +8% of VOCV by connecting a resistor between the CBC terminal and GND. This compensation voltage, VOCBC, represents the incremental increase in voltage, above the nominal no-load output voltage, needed to cancel or reduce the incremental decrease in voltage at the end of a cable due to its resistance. The programming resistance required for the desired cable compensation level at the converter output terminals can be determined using the equation below. As the load current changes, the cable compensation voltage also changes slowly to avoid disrupting control of the main output voltage. A sudden change in load current will induce a step change of output voltage at the end of the cable until the compensation voltage adjusts to the required level. Note that the cable compensation does not change the overvoltage protection (OVP) threshold,VOVP (see Electrical Characteristics), so the operating margin to OVP is less when cable compensation is used. If cable compensation is not required, CBC may remain unconnected.

Equation 30. UCC28730 qu29_lusbl5.gif