L6566ATR View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566ATR' PDF : 51 Pages View PDF
L6566A
Application information
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 L6566A 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 increases as a result of the feedback reaction to the energy delivery
stop (the output voltage is slowly decaying), the threshold is exceeded and the device
restarts switching again. In this way the converter works in burst-mode with a nearly
constant peak current defined by the internal disable level. A load decreases and then
causes a frequency reduction, which can go down even to a few hundred hertz, therefore
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.
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
Doc ID 13794 Rev 4
23/52
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