SCY99194 Datasheet, PDF (25/40 Pages) ON Semiconductor – Fixed Frequency Current Mode Controller

SCY99194
VHV
AC line unplug
X2 capacitor
discharge
X2 capacitor
discharge
AC line Unplug
detector starts
time
One Shot
No AC detection
tDET
tDET
DRV
Starts
only at
VCC(on)
time
DRV pulses stops
when VCC < VCC(off)
X2 discharge
current
X2 discharge
tDIS
X2 discharge ^time
tDIS
time
Figure 50. HV Pin ac Input Timing Diagram with X2 Capacitor Discharge Sequence When the Application is
Unplugged Under High Line and Light Load Condition
The Low Consumption Off Mode
There was implemented the low consumption off mode
allowing to reach extremely low no load input power as
described in previous chapters. If the voltage at feedback pin
decreases below the 0.4 V the controller enters the off mode.
The internal V_CC is turned−off, the IC consumes extremely
low V_CC current and only the voltage at external V_CC
capacitor is maintained by the Self−Supply circuit. The
Self−Supply circuit keeps the V_CC voltage at the V_CC(reg)
level. The supply for the FB pin watch dog circuitry and FB
pin bias is provided via the low consumption current sources
from the external V_CC capacitor. The controller can only
start, if the FB pin voltage increases above the 2.2 V level.
See Figure 51 for timing diagrams.
Only the X2 cap discharge and Self−Supply features is
enabled in the low consumption off mode. The X2 cap
discharging feature is enable due the safety reasons and the
DSS is enabled to keep the V_CC supply, but only very low
V_CC consumption appears in this mode. See the I_CC5
parameter in the electrical table. Any other features are
disabled in this mode.
The information about the latch status of the device is kept
in the low consumption off mode and this mode is used for
the TSD protection as well. The protection timer
GoToOffMode t_GTOM is used to protect the application
against the false activation of the low consumption off mode
by the fast drop outs of the FB pin voltage below the 0.4 V
level. E.g. in case when is present high FB pin voltage ripple
during the skip mode.
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