STMicroelectronics EVAL BOARD FOR L6563 EVL6563H-250W EVL6563H-250W Data Sheet
Product codes
EVL6563H-250W
Application information
L6563H
34/49
Doc ID 16047 Rev 3
Figure 48.
Interface circuits for power up sequencing when dc-dc has the SS
function
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
this prevents the dc-dc stage from starting up correctly) or, simply, the PWM controller is
devoid of soft start, the arrangement of
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.
UVLO thresholds of the PWM controller.
Figure 49.
Interface circuits for actual power-up sequencing (master PFC)
Another possible use of the RUN and PWM_STOP pins (again, in systems where the PFC
stage is the master) is the brownout protection, thanks to the hysteresis provided.
stage is the master) is the brownout protection, thanks to the hysteresis provided.
The brownout protection is basically a not-latched device shutdown function that is activated
when a condition of mains undervoltage is detected. This condition may cause overheating
of the primary power section due to an excess of RMS current. Brownout can also cause the
PFC pre-regulator to work open loop and this could be dangerous to the PFC stage itself
and the downstream converter, should the input voltage return abruptly to its rated value.
Another problem is the spurious restarts that may occur during converter power down and
that cause the output voltage of the converter not to decay to zero monotonically. For these
reasons it is usually preferable to shutdown the unit in case of brownout.
when a condition of mains undervoltage is detected. This condition may cause overheating
of the primary power section due to an excess of RMS current. Brownout can also cause the
PFC pre-regulator to work open loop and this could be dangerous to the PFC stage itself
and the downstream converter, should the input voltage return abruptly to its rated value.
Another problem is the spurious restarts that may occur during converter power down and
that cause the output voltage of the converter not to decay to zero monotonically. For these
reasons it is usually preferable to shutdown the unit in case of brownout.
IC shutdown upon brownout can be easily realized as shown in
. The scheme on
the left is of general use, that one on the right can be used if the bias levels of the multiplier
and the R
and the R
FF
·C
FF
time constant are compatible with the specified brownout level and with the
specified holdup time respectively. In this latest case, an additional resistor voltage divider
and one capacitor are not needed.
and one capacitor are not needed.
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