SLUP412 February 2022 LMG3522R030-Q1
While the CLLLC converter does an excellent job maintaining ZVS over a wide range of conditions, there are still many situations in which it cannot. Figure 7-2 shows several operating points that partially or even fully lose ZVS. The ability to maintain ZVS is complicated by the fact that a CLLLC converter uses frequency modulation as the primary control mechanism for maintaining output regulation. It turns out that most, if not all, of the conditions where the CLLLC converter loses ZVS are at a lighter load and at frequencies well above resonance (more on this later). The switching losses in these conditions will be proportional to that operating frequency. Fundamentally, if the operating frequency gets too high, the converter may overheat at a light load.