AN4027 datasheet(19/41 Pages) STMICROELECTRONICS

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DocID022604 Rev 3

19/41

AN4027

Functional check

In Figure 14 and Figure 15 the same images are captured during light load operation: note

that because of the resonant tank parameters, the half bridge transitions have similar rise

and fall times because the switched current is almost the same value in both load

conditions. In this case, the L6699 does not appreciably change the deadtime. In all

conditions it can be noted that both MOSFETs are turned on while resonant current is

flowing through their body diodes and drain-source voltage is zero, therefore achieving the

MOSFETs ZVS operation at turn-on.

In Figure 16 some signals at L6699 pins are measured. It can be seen that the signal on the

ISEN pin (#6) matches the instantaneous current flowing in the transformer primary side.

Contrary to the former resonant controllers such as the L6599A and others, requiring an

integration of current signal, the L6699 integrates the anti-capacitive mode protection,

therefore it needs to sense the instantaneous value of the current in order to check the

phase between the voltage and current. The LINE pin (#7) has been dimensioned to start up

the L6699 once the PFC output voltage has reached the rated value, in order to have

correct converter sequencing, with PFC starting first and LLC starting later in order to

Figure 14. HB transition at 0.25 A - rising edge Figure 15. HB transition at 0.25 A - falling edge

CH1: HB voltage

CH2: LVG

CH3: HVG

CH4: ISEN pin voltage

AM11407v1

CH1: HB voltage

CH2: LVG

CH3: HVG

CH4: ISEN pin voltage

AM11408v1

Figure 16. L6699 pin signals-1

Figure 17. L6699 pin signals-2

CH1: DIS

CH2: LINE

CH3: DELAY CH4: ISEN

AM11409v1

CH1: RFmin

CH2: STBY

CH3: CSS

CH4: CF

AM11410v1

AN4027 Datasheet(PDF) 19 Page - STMicroelectronics