SLUAAB9A March   2021  – December 2021 UCC25800-Q1

 

  1.   Trademarks
  2. 1 Introduction
  3. 2 Open-Loop LLC Converter Operation Principle
  4. 3 Primary-side and Secondary-side Resonant Configurations
  5. 4 Rectification Methods
    1. 4.1 One Resonant Capacitor, Voltage Doubler
    2. 4.2 Two Resonant Capacitors, Voltage Doubler
    3. 4.3 One Resonant Capacitor, Full-wave Rectifier
  6. 5  LLC Transformer Design Steps
    1. 5.1 Transformer Turns Ratio Selection
    2. 5.2 Transformer Volt-second Rating Calculation
    3. 5.3 Transformer Construction
    4. 5.4 Transformer Winding Selection
    5. 5.5 Transformer Inductance
      1. 5.5.1 Leakage inductance
      2. 5.5.2 Magnetizing inductance
    6. 5.6 Transformer Selections
  7. 6 Negative Voltage Generation
    1. 6.1 Using a Zener Diode
    2. 6.2 Using a Shunt Regulator
    3. 6.3 Using a Shunt Regulator and Linear Regulator
  8. 7 Multiple-output Design
    1. 7.1 One UCC25800-Q1 Drives Each Output
    2. 7.2 Transformer With Multiple Secondary-side Windings
    3. 7.3 Multiple Transformers
  9. 8 EMI Performance
    1. 8.1 EMI Performance With Standalone Converter
    2. 8.2 EMI performance with an inverter power stage
  10. 9 Common-Mode Transient Immunity (CMTI)
  11. 10Summary
  12. 11Revision History

1 Introduction

UCC25800-Q1 is an open-loop LLC transformer driver. By open-loop control, fixed output to input voltage gain can be achieved through the transformer turns ratio. The open-loop control also provides a simple design and superior noise immunity. The LLC topology utilizes the transformer leakage inductance as its resonant component, allowing the converter to use a transformer with a larger leakage inductance but a much smaller primary-side to secondary-side parasitic capacitance (inter-winding capacitance).

Other topologies, such as flyback or push-pull, require minimum leakage inductance to improve the efficiency, reduce the voltage and current stress, as well as minimize the noise created by the converter. In turn, this type of transformer suffers from larger inter-winding capacitance. When they are used in the gate driver bias supply applications, the high dv/dt from the inverter power stage can be coupled through the transformer inter-winding capacitance to the low-voltage side. This creates a much more severe EMI noise issue. It also puts more challenges on the common-mode transient immunity (CMTI). The open-loop LLC transformer driver solves this issue and provides a low-noise, robust solution for the isolated gate driver bias supplies.