Datasheet

L6591 Application information
Doc ID 14821 Rev 6 25/41
Figure 43. Load-dependent operating modes: timing diagram
Figure 44. Addition of an offset to the current sense lowers the burst mode
operation threshold
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 L6591 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 L6591 provides the PFC_STOP (#8) pin: it is an open collector 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 45 . When the L6591 is in UVLO, the pin is kept open, to let the PFC controller start
first.
AM13259v1
LVG, HVG
1.82V
t
t
t
COMP
edom-tsruBedoM.qerF.xiF
fosc
Fix. Freq .Mode
PF C _STO P
PFC
GATE-DR IVE
1.75V
AM13260v1
Rs
L6591
R
Vref
Rc
6
10
4
11
V
o
= Vref
R
R + Rc
LVG
ISEN
GND
Rs
L6591
R
Vref
Rc
6
10
4
11
V
o
= Vref
R
R + Rc
LVG
ISEN
GND