SLUAAQ7A August   2023  – April 2025 UCC256404

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Theory of LLC Topology Design
  6. 3Burst Mode Operating Control Mechanism
  7. 4Potential ZCS Issue When Exiting Burst Mode
  8. 5Design to External Circuit for Solving ZCS Issue at Burst Transition Period
  9. 6Design to Accurate External Circuit for Solving ZCS Issue at Burst Transition Period_(Option)
    1. 6.1 Test Result of External Circuit for Solving ZCS Issue at Burst Transition Period
  10. 7Summary
  11. 8References
  12. 9Revision History

1 Introduction

At the time of writing this application note, the current requirement for TV’s to meet DoE Level Vi and CoC Tier 2 standards is to consume less than 500mW of standby power when the TV is off. Because the LLC topology has a limited frequency range where it can achieve resonance, at light load the best option is to enter into burst mode to minimize power consumption. The UCC256404 employs a soft-in and soft-out of burst mode to help minimize audible noise. The challenge with entering into and out of burst mode is to ensure that under all conditions that Zero Current Switching (ZCS) is avoided. ZCS or hard switching is an unwanted operating mode for an LLC and may result in circuit failures. The purpose of this application note is to show how to dynamically adjust standby power performance in burst mode.