L6566A View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566A' PDF : 52 Pages View PDF
Application information
Figure 18. Hiccup-mode OCP: timing diagram
Vcc
(pin 5)
VccON
Secondary diode is shorted here
VccOFF
Vccrestart
VCS
1.5 V
(pin 7)
GD
(pin 4)
OCP latch
Vcc_OK
Vcc_PFC
(pin 6)
L6566A
t
t
t
t
t
t
5.8
PFC interface
The device is specifically designed to minimize converter losses under light or no-load
conditions, and a special function has been provided to help the designer meet energy
saving requirements even in power-factor-corrected systems where a PFC pre-regulator
precedes the isolated DC-DC converter.
In fact, EMC regulations require compliance with low-frequency harmonic emission limits at
nominal load; no limit is envisaged when the converter operates with a light load. Then the
PFC pre-regulator can be turned off, therefore saving the no-load consumption of this stage
(0.5÷1 W).
To do so, the L6566A provides the Vcc_PFC pin (6): this pin is internally connected to the
Vcc pin (5) via a PNP transistor, normally closed, that opens when the voltage VCOMP falls
below VCOMPO, a threshold internally set at a value depending on whether QR operation or
FF operation is selected. This pin is intended for supplying the PFC controller of the pre-
regulator as shown in Figure 16. The switch is thermally protected, so that the IC stops if an
external failure causes the pin to be overloaded for too long a time or shorted to ground.
30/52
Doc ID 13794 Rev 4
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