NCP1238
http://onsemi.com
19
To reduce the power dissipation in case the V
CC
pin is
shorted to GND (in case of V
CC
capacitor failure, or external
pulldown on V
CC
to disable the controller), the startup
current is lowered when V
CC
is below V
CC(inhibit)
.
There are only two conditions for which the current source
doesn’t turn on when V
CC
reaches V
CC(min)
: the voltage on
HV pin is too low (below V
HV(min)
), or a thermal shutdown
condition (TSD) has been detected. In all other conditions,
the HV current source always turns on and off to maintain
V
CC
between V
CC(min)
and V
CC(on)
.
Brown−out and Line Overvoltage
When the input voltage goes below V
HV(stop)
, a
brown−out condition is detected, and the controller stops.
The HV current source alternatively turns on and off to
maintain V
CC
between V
CC(on)
and V
CC(min)
until the input
voltage is back above V
HV(start)
.
The same situation occurs when an overvoltage is
detected on the ac line, i.e. when the input voltage goes
above V
HV(OV)
: the controller stops, and resumes normal
operation when the overvoltage condition has gone.
Figure 43. Brown−out or Line Overvoltage Timing Diagram
time
HV stop
time
V
CC
time
DRV
V
CC(on)
V
CC(min)
Waits next
V
CC(on)
before
starting
Brown-out
or AC OVP
detected
