Datasheet

UCC25600

SLUS846B –SEPTEMBER 2008– REVISED JULY 2011

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Burst-Mode Operation

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 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, 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 over voltage 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 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 350kHz and burst mode operation will

not occur.