Functional check

AN3233

16/35

Doc ID 17595 Rev 1

In Figure 13 it can be noted that the resonant current at turn-on has some oscillations due to

the charging of the resonant elements. However, current zero-crossing always lags the HB

commutations and, consequently, MOSFETs are soft switched.

Figure 14

shows the resonance current at shutdown. Due to input voltage dip, the LLC stage

operates below resonance, but current still lags the HB voltage.

Avoiding hard switching also during transitions like startup and shutdown is a must for a

reliable design, because some hard switching commutations could also damage the

converter.

No-load operation

In Figure 15 and 16, some burst mode waveforms are captured. As seen, both L6599A and

L6563H operate in burst mode. In Figure 16, it is possible to see that PFC and LLC bursts

are synchronized

.

Figure 13.

Startup resonant current

Figure 14.

Shutdown resonant current

CH1: Half-bridge

CH3 C6 voltage

CH1: Half-bridge

CH4: Res. tank current

CH4: Res. tank current

Figure 15.

No-load operation

Figure 16.

No-load operation – detail

CH1: LVG pin

CH2: PFC gate

CH1: Half-bridge

CH2: PFC Drain

CH3: Output voltage

CH4: STBY pin

CH3: PFC-STOP pin

CH4: STBY pin