L6563H datasheet(33/48 Pages) STMICROELECTRONICS

33 / 48 page

L6563H

Application information

Doc ID 16047 Rev 2

33/48

Figure 47.

Interface circuits that let the L6563H 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 48

. 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 L6563H.

Figure 48.

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 49 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.

L6563H Datasheet(PDF) 33 Page - STMicroelectronics