VIPER53-E STMicroelectronics, VIPER53-E Datasheet - Page 24

• Manufacturer Part Number: VIPER53-E
• Description: Fixed frequency off line converter
• Manufacturer: STMicroelectronics

Short-circuit and overload protection
10
24/36
Short-circuit and overload protection
A V
V
When reaching typically V
stops switching. This state is latched because of to the regulation loop which maintains the
COMP pin voltage above the V
more energy from the auxiliary winding, its voltage drops down until it reaches V
the device is reset, recharging the V
drops below the V
resumes switching immediately.
The device enters an endless restart sequence if the overload or short circuit condition is
maintained. The restart duty cycle D
to restart, thus delivering its full power capability to the output. In order to keep the whole
converter in a safe state during this event, D
compromising the real start-up of the converter. A typical value of about 10% is generally
sufficient. For this purpose, both V
following conditions:
Equation 6
Equation 7
Refer to the previous start-up section for the definition of tss, and C
checked against the limit given in this section. The maximum value of the two calculus will
be adopted.
All this behavior can be observed on
of the drain current Id for V
is the drain current to take into account for design purposes. Since I
maximum value for which the overload protection is not triggered, it defines the power
capability of the power supply.
COMP
COMPovl
goes above this level, the capacitor connected on the TOVL pin begins to charge.
threshold of about 4.35V has been implemented on the COMP pin. When
COMPovl
C
OVLth
VDD
threshold for any reason during the VDD drop, the device
COMP
COMPovl
(4V), the internal MOSFET driver is disabled and the device
8
= V
DD
C
10
RST
OVL
DD
COMPovl
Figure 8 on page
4
and TOVL capacitors can be used to satisfy the
threshold. Since the V
capacitor for a new restart cycle. Note: If VCOMP
is defined as the time ratio for which the device tries
12.5
------------- - 1
D
RST
1
RST
is shown. The corresponding parameter I
–
10
must be kept as low as possible, without
–
6
C
-------------------------------------- -
10. In
tss
OVL
V
DDhyst
Figure 10 on page 11
I
DD
DDch2
pin does not receive any
VDD
Dmax
must also be
represents the
VIPer53 - E
DDoff
the value
and
Dmax