viper31sp STMicroelectronics, viper31sp Datasheet - Page 13

• Manufacturer Part Number: viper31sp
• Description: Battery Charger Primary I.c.
• Manufacturer: STMicroelectronics

this value to provide a soft start feature, of which
the duration depends on some circuit parameters,
like transformer ratio, sense resistor, output
capacitors and load. The user will define the best
appropriate value by experiments.
SHORT CIRCUIT OPERATION
In case of abnormal condition where the auxiliary
winding is unable to provide the low voltage
supply current to the V
the output of the converter), the external
capacitors discharge themselves down to the low
threshold voltage V
the device get back to the inactive state where the
internal circuits are in standby mode and the start
up current source is activated. The converter
enters a endless start up cycle, with a start-up
Figure 13: Start Up Circuit and Sequence
Figure 14 : Short circuit operation
AUXILIARY
WINDING
C
VCC
C
VDD
VCC
VDD
DD
off of the UVLO logic, and
CC
LDO
Reg.
GND
pin (i.e. short circuit on
ON/OFF
Ref
VDDon
VDDoff
UVLO LOGIC
VIPer31
Isc
2 mA
+
-
VDD
Iout
SOURCE
DRAIN
output current
duty cycle defined by the ratio of charging current
towards discharging when the VIPer31 tries to
start. This ratio is fixed by design to 1.5 to 12,
which gives a 11% start up duty cycle, while the
power dissipation at start up is approximately 0.6
W, for a 230 Vrms input voltage.
The average output short circuit current is the
product of the start up duty cycle by the output
current flowing during the active phase of the
device (See figure 14). This output current is
limited by either the CREF pin voltage, or the
internal current limitation of 1.3 A. These values
together with the low value of start-up duty cycle
prevents the stress of the output rectifiers and of
the transformer when in short circuit.
Average
VDDreg
VDDon
VDDoff
(V)
SC12160
t
t
tss
SC12150
VIPer31SP
VCC
VDD
13/16
t