L6566A View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566A' PDF : 52 Pages View PDF
Application information
L6566A
5.11
OVP block
The OVP function of the L6566A monitors the voltage on the ZCD pin (11) in the MOSFET
OFF-time, during which the voltage generated by the auxiliary winding tracks the converter
output voltage. If the voltage on the pin exceeds an internal 5 V reference, a comparator is
triggered, an overvoltage condition is assumed and the device is shut down. An internal
current generator is activated that sources 1 mA out of the VFF pin (15). If the VFF voltage
is allowed to reach 2 Vbe over 5 V, the L6566A is latched off. See Section 5.9 for more
details on the IC’s behavior under these conditions. If the impedance externally connected
to pin 15 is so low that the 5+2 VBE threshold cannot be reached or if some means is
provided to prevent that, the device is able to restart after the Vcc has dropped below 5 V.
Refer to Section 6 (Table 7) for additional hints.
Figure 22. OVP function: internal block diagram
PWM latch
RQ
SQ
to triggering
block
ZCD
11
5V
40kΩ
-
+
5pF
COUT
L6566A
Monostable
M1
2 µs
Monostable STROBE
M2
0.5 µs
OVP
FF
R Q1
S
2-bit
counter
Fault
Counter
reset
Figure 23. OVP function: timing diagram
GD
(pin 4)
Vaux
t
0
ZCD
(pin 11)
t
5V
COUT
t
STROBE
2 µs
0.5 µs
t
t
OVP
COUNTER
RESET
COUNTER
STATUS
0
0
FAULT
t
t
0
0 →1
1 →2
2 →0
0
0 →1
1 →2
2 →3
3 →4
t
Vcc_PFC
(pin 6)
NORMAL OPERATION
TEMPORARY DISTURBANCE
t
FEEDBACK LOOP FAILURE
t
34/52
Doc ID 13794 Rev 4
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