L6563S datasheet(32/42 Pages) STMICROELECTRONICS

32 / 42 page

Application information

L6563S

32/42

Doc ID 16116 Rev 3

Figure 44.

Interface circuits that let the L6563S switch on or off a PWM controller

If the chip is provided with a soft-start pin, it is possible to delay the start-up of the dc-dc

stage with respect to that of the PFC stage, which is often desired, as described in

Figure 45

. An underlying assumption in order for that to work properly is that the UVLO

thresholds of the PWM controller are certainly higher than those of the L6563S.

Figure 45.

Interface circuits for power up sequencing when dc-dc has the SS

function

If this is not the case or it is not possible to achieve a start-up delay long enough (because

this prevents the dc-dc stage from starting up correctly) or, simply, the PWM controller is

devoid of soft start, the arrangement of Figure 46 lets the dc-dc converter start-up when the

voltage generated by the PFC stage reaches a preset value. The technique relies on the

UVLO thresholds of the PWM controller.

L6563S Datasheet(PDF) 32 Page - STMicroelectronics