VIPer12ADIP / VIPer12AS
Figure 11 : Start Up Sequence
Figure 12 : Overvoltage Sequence
V
DD
V
DD
VDDon
V
DDovp
VDDoff
V
DDon
tss
V
DDoff
t
t
t
t
V
I
FB
DS
t
V
OUT
OVERVOLTAGE THRESHOLD
An overvoltage detector on the VDD pin allows the
VIPer12A to reset itself when VDD exceeds
VDDovp. This is illustrated in figure 12, which shows
the whole sequence of an overvoltage event. Note
that this event is only latched for the time needed
by VDD to reach VDDoff, and then the device
resumes normal operation automatically.
the regulation point where the secondary loop
begins to send a current in the optocoupler. At this
point, the converter enters a regulated operation
where the FB pin receives the amount of current
needed to deliver the right power on secondary
side.
This sequence is shown in figure 11. Note that
during the real starting phase tss, the device
consumes some energy from the VDD capacitor,
waiting for the auxiliary winding to provide a
continuous supply. If the value of this capacitor is
too low, the start up phase is terminated before
receiving any energy from the auxiliary winding
and the converter never starts up. This is illustrated
also in the same figure in dashed lines.
10/15
STMICROELECTRONICS [ ST ]
