Datasheet

L6699 Operation at no load or very light load
Doc ID 022835 Rev 2 23/38
Figure 17. How the L6699 can switch off a PFC controller at light load
To help the user meet energy saving requirements even in power-factor-corrected systems,
where a PFC pre-regulator precedes the DC-DC converter, the L6699 allows that the PFC
pre-regulator can be turned off during burst-mode operation, therefore eliminating the no
load consumption of this stage (0.5
- 1 W). There is no compliance issue in that, because
EMC regulations on low-frequency harmonic emissions refer to nominal load, no limit is
envisaged when the converter operates with light or no load.
To do so, the L6699 provides pin 8 (PFC_STOP): it is an open drain output, normally open,
that is asserted low when the IC is idle during burst-mode operation. This signal is externally
used for switching off the PFC controller and the pre-regulator as shown in
Figure 17 . When
the L6699 is in UVLO the pin is kept open to allow the PFC controller to start first.
The PFC_STOP pin is also used by some protection functions (OCP, OLP and latched
shutdown). Please refer to the relevant sections for more information.
AM11388v1
L6699
PFC_STOP9
L6563S/H
L6564, L6564T/H
L4984
PFC_OK
(AC_OK)
L6699
PFC_STOP
9
L6562/2A
12
Vcc
ZCD (L6562)
INV (L6562A)
22 k
W
100 k
W
BC547
BC547