NCP1927 Datasheet, PDF (11/24 Pages) ON Semiconductor – Combination Power Factor Correction Controller and Flyback Controller for Flat

NCP1927
Vin
Rstart
D1
D2
+ _C1 + _C2
Aux Winding
ICC
VCC
NCP1927
Figure 3. Operation with Dual V_CC Capacitors
V_CC
V_CC(on)
V_CC(off)
V_CC(reset)
0V
DRV
PDRV
PDRV
Time
FDRV
FDRV
I_CC
I_CC1+I_CC(FDRV)+I_CC(PDRV)
I_CC3+_ICC(FDRV)
I_CC5
Time
Time
Figure 4. Startup Sequence of the NCP1927
VCC
VCCON
VCCOFF
Fault
Occurs
DRV
Device
Restarts
Fault is Reset
time
ICC
ICC2
time
ICC4
ICC5
time
Figure 5. V_CC During a V_CC Hiccup
SHUTDOWN PIN
The Shutdown pin allows for external disabling of the
NCP1927. When V_Shutdown is pulled above the shutdown
threshold, V_SHDN (typically 1.0 V), both the flyback and
PFC drive outputs are immediately turned off, and a V_CC
hiccup occurs (see Figure 5). When V_CC reaches V_CC(on),
the cycle repeats unless the NCP1927 is taken out of
shutdown. This is achieved when V_Shutdown becomes less
than V_SHDN. The NCP1927 leaves shutdown mode and will
start when V_CC reaches V_CC(on) according to the initial
power−on sequence. The V_CC behavior during shutdown
mode is shown in Figure 6.
FAULT MANAGEMENT
When the NCP1927 detects a non−latching fault
(Shutdown Mode, TSD, and Flyback Overload), the drivers
are disabled, and V_CC falls towards V_CC(off) due to the IC
internal current consumption. Once V_CC falls below
V_CC(off), the fault is reset and the IC internal current
consumption is reduced to the startup current, I_CC5. V_CC
begins to rise as if power was initially applied and the device
resumes normal operation once V_CC reaches V_CC(on). This
cycle between V_CC(on) and V_CC(off) is commonly referred to
as a V_CC hiccup and is shown in Figure 5.
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