SCY99194 Datasheet, PDF (19/40 Pages) ON Semiconductor – Fixed Frequency Current Mode Controller

SCY99194
For safety reasons, the start−up current is lowered when
V_CC is below V_CC(inhibit), to reduce the power dissipation in
case the V_CC pin is shorted to GND (in case of V_CC capacitor
failure, or external pull−down on V_CC to disable the
controller). There is only one condition for which the current
source doesn’t turn on when V_CC reaches V_CC(inhibit): the
voltage on HV pin is too low (below V_HV(min)). The
controller can restart only when VCC reaches VCC(on) and
VHV
HV pin slope
S_HV is positive
when the slope on HV pin is positive during the short ac line
drop−outs. This feature differentiates between the short ac
line drop−outs and application plug off. The minimum
positive slope is defined by the Equation 1 in following
chapter.
Ac line drop−out
VCC
V_CC(on)
V_CC(min)
V_CC(off)
Controller stops
at V_CC(off)
V_CC charges
up when V_HV
is high enough
DRV
Switching
restarts at
V_CC(on) and
positive S_HV
Output
V_OUT
Loss of
regulation when
V_HV is too low
Figure 44. Ac Line Drop−out Timing Diagram
time
time
time
time
http://onsemi.com
19