L6566B View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566B' PDF : 51 Pages View PDF
Application information
L6566B
5.3
Note:
Burst-mode operation at no load or very light load
When the voltage at the COMP pin (9) falls 20 mV below a threshold fixed internally at a
value, VCOMPBM, depending on the selected operating mode, the L6566B is disabled with
the MOSFET kept in OFF state and its consumption reduced at a lower value to minimize
Vcc capacitor discharge.
The control voltage now will increase as a result of the feedback reaction to the energy
delivery stop (the output voltage will be slowly decaying), the threshold will be exceeded and
the device will restart switching again. In this way the converter will work in burst-mode with
a nearly constant peak current defined by the internal disable level. A load decrease will
then cause a frequency reduction, which can go down even to few hundred hertz, thus
minimizing all frequency-related losses and making it easier to comply with energy saving
regulations. This kind of operation, shown in the timing diagrams of Figure 11 along with the
others previously described, is noise-free since the peak current is low.
If it is necessary to decrease the intervention threshold of the burst-mode operation, this can
be done by adding a small DC offset on the current sense pin as shown in Figure 12 on
page 25.
The offset reduces the available dynamics of the current signal; thereby, the value of the
sense resistor must be determined taking this offset into account.
Figure 11. Load-dependent operating modes: timing diagrams
COMP
(pin 9)
VCOMPBM
20 mV
hys ter.
fosc
fsw
GD
(pin 4)
MODE/SC=Open
MODE/SC=VREF
FF Mode
QR Mode
Burs t-m ode
Burs t-m ode
Valley-skipping Mode
t
MODE/SC=Open
MODE/SC=VREF
t
FF Mode
t
QR Mode
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