L6566BH View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566BH' PDF : 51 Pages View PDF
L6566BH
Application information
overload, the system has a power capability lower than that at nominal load but the output
current may be quite high and can overstress the output rectifier. In the case of FF operation
the capability is almost unchanged and both short-circuit and overload conditions are more
critical to handle.
The L6566BH, regardless of the operating option selected, makes it easier to handle such
conditions: the 2 V clamp on the SS pin is removed and a second internal current generator
ISS2 = ISS1 /4 continues to charge CSS. As the voltage reaches 5 V the device is disabled, if
it is allowed to reach 2 VBE over 5 V, the device is latched off. In the former case the
resulting behavior is identical to that of short-circuit illustrated in Figure 7; in the latter case
the result is identical to that of Figure 20. See Section 5.9: Latched disable function for
additional details.
Figure 21. Soft-start pin operation under different operating conditions and settings
Vcc
(pin 5)
SS 5V+2Vbe
(pin 14) 5V
2V
COMP
(pin 9)
Vcc falls below UVLO
before latching off
here the IC
shuts down
here the IC
latches off
UVLO
t
t
GD
(pin 4)
t
START-UP
NORMAL
OPERATION
TEMPORARY
OVERLOAD
NORMAL
OPERATION
OVERLOAD
SHUTDOWN
LATCHED
AUTORESTART
t
RESTART
Note:
AM11497v1
A diode, with the anode to the SS pin and the cathode connected to the VREF pin (10), is
the simplest way to select either auto-restart mode or latch-mode behavior upon
overcurrent. If the overload disappears before the Css voltage reaches 5 V, the ISS2
generator is turned off and the voltage gradually brought back down to 2 V. Refer to
Section 6: Application examples and ideas (Table 7) for additional information.
If latch-mode behavior is desired also for converter short-circuit, make sure that the supply
voltage of the device does not fall below the UVLO threshold before activating the latch.
Figure 21 shows soft-start pin behavior under different operating conditions and with
different settings (latch-mode or auto-restart).
Unlike other PWM controllers provided with a soft-start pin, in the L6566BH grounding the
SS pin does not guarantee that the gate driver is disabled.
5.11
OVP block
The OVP function of the L6566BH monitors the voltage on the ZCD pin (11) in MOSFET
OFF-time, during which the voltage generated by the auxiliary winding tracks the converter’s
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
Doc ID 16610 Rev 2
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