DocID027367 Rev 3

11/22

SRK2001

Operation description

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Figure 7. Full load and light-load turn-on

At the start-up and on sleep mode exiting, the control circuit starts with a turn-on delay set to

30% of the clock cycle and progressively adapts it to the proper value. This allows reducing

system perturbation both during the start-up and while exiting the sleep mode during a fast

zero to full load transition. After the turn-on, a blanking time (equal to 50% of the clock

period) masks an undesired turn-off due to the drain-source voltage drop, consequent to

MOSFET switch on (flowing current passes from the body diode to MOSFET channel

resistance).

5.3

Turn-off

The SR MOSFET turn-off may be triggered by an adaptive turn-off mechanism (two slope

turn-off) or by the ZCD_OFF comparator (fast turn-off, see Section 5.4).

stray inductance), the sensed drain-source signal is not really equal to the voltage drop

zero, causing a premature MOSFET turn-off.

To overcome this problem (without adding any stray inductance compensation circuit), the

device uses a turn-off mechanism based on an adaptive algorithm that turns off the SR

MOSFET when the sensed drain voltage reaches zero adapting progressively the turn-off to

the maximum conduction period.