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

5 Design to External Circuit for Solving ZCS Issue at Burst Transition Period

The auto standby circuitry below makes sure that the minimum burst off is 200µs when the switching node is damped, and the first pulse of the burst packet turns on without ZCS. Figure 5-1 shows how to minimize the ZCS issue at burst transition period with auto standby external circuit.

The following list details the operating mechanism for external auto standby circuit with the UCC256404.

  1. Use circuit to automatically turn on PFC and disable burst mode at higher load condition.
  2. INA boosts voltage across current sense on output power rail
  3. Comparator output is high when INA output is greater than reference voltage, Small FET turn on sends fault signal to primary side at LL/SS pin.
  4. Disables burst mode as load gets larger to make sure minimum time is kept between burst packets
External Auto Standby Circuit With UCC256404Figure 5-1 External Auto Standby Circuit With UCC256404