During light load condition, the resonant converter tends to increase its switching frequency and maintain the output voltage regulation. However, due to ringing caused by the transformer parasitic capacitor and the rectification-diode-junction capacitors, the energy could be directly transferred to the load through these capacitors. When this power becomes more than the load requires, the output voltage become higher than the regulation level. In this case, further increasing the switching frequency will not help the situation because energy transfer to the load is not through the power stage itself.

To prevent output overvoltage during this condition, the UCC25600 includes the burst-mode operation function. When the control loop demands switching frequency higher than 350 kHz, the gate driver is disabled and the power stage stops switching. When the output voltage drops, the control loop begins to demand switching frequency less than 330 kHz, the gate driver recovers and the power stage begins to deliver power again. This allows the output voltage to be regulated.

This burst mode can be easily disabled by limiting the maximum switching frequency to less than 350 kHz. In this way, the control loop will never demand a switching frequency higher than 350 kHz and burst mode operation will not occur.