viper53esp STMicroelectronics, viper53esp Datasheet - Page 15

• Manufacturer Part Number: viper53esp
• Description: Off-line Primary Switch
• Manufacturer: STMicroelectronics

VIPer53EDIP - E / VIPer53ESP - E
9
Short-Circuit and Overload Protection
A V
goes above this level, the capacitor connected on the TOVL pin begins to charge. When
reaching typically V
switching. This state is latched because of to the regulation loop which maintains the COMP
pin voltage above the V
energy from the auxiliary winding, its voltage drops down until it reaches V
device is reset, recharging the V
below the VCOMPovl threshold for any reason during the VDD drop, the device 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:
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
the drain current Id for V
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.
COMPovl
threshold of about 4.4V has been implemented on the COMP pin. When V
OVLth
COMPovl
COMP
(4V), the internal MOSFET driver is disabled and the device stops
C
VDD
= V
threshold. Since the V
DD
8 10
COMPovl
DD
C
capacitor for a new restart cycle. Note: If VCOMP drops
DocRev1
RST
Figure 2 on page
OVL
and TOVL capacitors can be used to satisfy the
4
is defined as the time ratio for which the device tries
⎛
------------- - 1
D
12.5 10
is shown. The corresponding parameter I
RST
1
RST
–
must be kept as low as possible, without
–
⎞
⎠
Short-Circuit and Overload Protection
6
C
------------------------------------
tss
DD
7. In
OVL
V
DDhyst
pin does not receive any more
Figure 7 on page 20
I
D Dch2
Dmax
VDD
represents the
must also be
DD
off and the
the value of
Dmax
COMP
15/31
is