viper31sp STMicroelectronics, viper31sp Datasheet - Page 14

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

VIPer31SP
OVERVOLTAGE PROTECTION
If the output voltage accuracy is not a concern,
but only a limitation is desired, the internal
overvoltage protection can be used. In this case,
five components can be taken out from the
schematics of figure 10 (R3-R10-R6-C4-C5) and
the input pin FB of the error amplifier is simply
grounded. The internal overvoltage protection will
act as soon as the V
29 V, by turning off the power mosfet switch. An
hysteresis of about 3 V will enable again the
switching of the device at a lower voltage level on
the V
limitation, in a burst mode operation type, with
some ripple on the output. Case by case
experiments will define the correct value of output
capacitor C3, according to the loading current in
low output power condition.
STANDBY MODE
The standby mode is represented by a very low
output current, corresponding to a full loaded
battery in a battery charger application. The
output voltage is limited by either the overvoltage
14/16
CC
pin. This results in an efficient voltage
CC
voltage reaches typically
protection or the error amplifier, according to the
design. This results into different situations :
-
-
Note that the burst operation is providing a very
low input power consumption, because it reduces
the switching frequency, and thus commutation
losses. Less than 1 W of input power can be
observed in this operative mode, with a few
hundreds of mW delivered to the secondary load.
This is far compliant with standby standards, like
the ”Blue Angel” one.
In case the overvoltage protection is used, the
burst mode operation as described previously
takes place, governed by the hysteresis of the
overvoltage comparator.
If the error amplifier is used, many situation can
occur, depending on the compensation network
foreseen by the designer. These situations can
range from a normal continuous operation, to
burst mode. In any case, the output voltage will
be regulated to the desired value.