SLUSC60B December   2017  – October 2019 UCC28064A


  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Simplified Application
  4. Revision History
  5. Description (Continued)
  6. Pin Configuration and Functions
    1.     Pin Functions
  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. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Principles of Operation
      2. 8.3.2  Natural Interleaving
      3. 8.3.3  On-Time Control, Maximum Frequency Limiting, Restart Timer and Input Voltage Feed-Forward compensation
      4. 8.3.4  Distortion Reduction
      5. 8.3.5  Zero-Current Detection and Valley Switching
      6. 8.3.6  Phase Management and Light-Load Operation
      7. 8.3.7  Burst Mode Operation
      8. 8.3.8  External Disable
      9. 8.3.9  Improved Error Amplifier
      10. 8.3.10 Soft Start
      11. 8.3.11 Brownout Protection
      12. 8.3.12 Line Dropout Detection
      13. 8.3.13 VREF
      14. 8.3.14 VCC
      15. 8.3.15 System Level Protections
        1. Failsafe OVP - Output Over-voltage Protection
        2. Overcurrent Protection
        3. Open-Loop Protection
        4. VCC Undervoltage Lock-Out (UVLO) Protection
        5. Phase-Fail Protection
        6. CS - Open, TSET - Open and Short Protection
        7. Thermal Shutdown Protection
        8. Fault Logic Diagram
    4. 8.4 Device Functional Modes
  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.  Custom Design With WEBENCH® Tools
        2.  Inductor Selection
        3.  ZCD Resistor Selection RZA, RZB
        4.  HVSEN
        5.  Output Capacitor Selection
        6.  Selecting RS For Peak Current Limiting
        7.  Power Semiconductor Selection (Q1, Q2, D1, D2)
        8.  Brownout Protection
        9.  Converter Timing
        10. Programming VOUT
        11. Voltage Loop Compensation
      3. 9.2.3 Application Curves
        1. Input Ripple Current Cancellation with Natural Interleaving
        2. Brownout Protection
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Package Option Addendum
    1. 12.1 Packaging Information
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Development Support
        1. Custom Design With WEBENCH® Tools
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Community Resources
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

Burst Mode Operation

To further improve light load efficiency burst mode operation can be used. In this case the burst mode threshold is fed to BRST pin by an external source that could be a simple resistor divider connected to the VREF pin. If COMP pin voltage goes below the BRST pin voltage the converter stops switching. When the COMP voltage exceeds BRST pin voltage plus hysteresis, the converter restarts switching.

In order to have a smooth transition between switching and not switching and vice-versa burst soft-on and burst soft-off features are added. So when the COMP voltage goes below BRST voltage switching is not stopped immediately, but there will be eight additional switching cycles where FET on time is decreased gradually. In similar way when COMP voltage exceeds BRST voltage plus hysteresis a soft-on period occurs where the on time is increased gradually to a value that corresponds to the present COMP voltage in eight switching cycles.

When the load decreases the device is intended to operate in single phase mode starting from 35% to 15% of rated load and goes to burst mode at lower load values when single phase operation is activated. If the PHB threshold is lower than the Burst mode threshold, single phase operation is forced during soft-on and soft-off periods of burst mode.

Similar to the PHB feature the burst mode threshold has two different levels depending if the PFC input voltage is in the range of 90 to 132 VRMS (US main) or in the range of 180 to 265 VRMS (European main). If the peak voltage on VINAC pin peak voltage exceeds 3.5 V (typ.) a small current (3 µA typically) is provided from BRST pin. If a resistor divider is used to set the BRST pin voltage this current will raise the voltage.

Use Equation 11 and Equation 12 to calculate the resistor divider that sets the Burst Mode thresholds. These equations are identical to the equations used to calculate the PHB resistor divider.

RU and RD are the upper and the lower resistence of the resistor divider connected to VREF pin.

Equation 11. UCC28064A eq_ru_slusde9.gif
Equation 12. UCC28064A eq_rd2_slusde9.gif