NCP1271 ON Semiconductor, NCP1271 Datasheet - Page 11

• Manufacturer Part Number: NCP1271
• Description: Soft?skip? Mode Standby Pwm Controller With Adjustable Skip Level And External Latch
• Manufacturer: ON Semiconductor

external components during a fault event. After the second
cycle, the controller tries to restart the application. If the
restart is not successful, then the process is repeated.
During this mode, V
reset level. Therefore, latched faults will not be cleared
unless the application is unplugged from the AC line (i.e.,
V
hiccup operation. Note that at each restart attempt, a soft
start is issued to minimize stress.
V
when the feedback pin is open (i.e. FB is greater than 3 V)
for 130 ms or V
Therefore, to take advantage of these features, the V
capacitor needs to be sized so that operation can be
maintained in the absence of the auxiliary winding for at
least 130 ms.
frequency with a 1 nF switch gate capacitance. Therefore,
to ensure at least 130 ms of operation, equation 1 can be
used to calculate that at least an 85 mF capacitor would be
necessary.
capacitance value needs to at least be large enough for the
output to charge up to a point where the auxiliary winding
can supply V
scenarios with different V
cap is too small, the application fails to start because the
bias supply voltage cannot be established before V
reduced to the V
12.6 V
9.1 V
5.8 V
t startup +
bulk
CC
Figure 25 shows a timing diagram of the V
As stated earlier, the NCP1271 enters a fault condition
The controller typically consumes 2.3 mA at a 65 kHz
If the 130 ms timer feature will not be used, then the
Figure 25. V
Capacitor
discharges).
Supply voltage, V
Drain current, I
C VCC DV
I CC1
CC
CC
CC(off)
CC
. Figure 26 describes different startup
Double Hiccup Operation in a Fault
drops below V
D
CC
+
CC
t startup
Condition
level.
85 mF · (12.6 V-9.1 V)
never drops below the 4 V latch
CC
capacitor values. If the V
Switching is missing in
every two V
featuring a “double-hiccup”
2.3 mA
CC(off)
CC
(9.1 V typical).
hiccup cycles
+ 130 ms
CC
double
http://onsemi.com
time
(eq. 1)
time
CC
CC
CC
NCP1271
is
11
close as possible to the V
to reduce switching noise. A small bypass capacitor on this
pin is also recommended. If the switching noise is large
enough, it could potentially cause V
and force a restart of the controller.
winding bias voltage and V
transient swings of the auxiliary winding are allowed. In
standby mode, the V
the low-frequency skip-cycle operation. The V
capacitor also affects this swing. Figure 27 illustrates the
possible swings.
12.6 V
12.6 V
9.1 V
0.6 V
9.1 V
5.8 V
0.6 V
It is highly recommended that the V
It is also recommended to have a margin between the
Figure 27. Timing Diagram of Standby Condition
Supply voltage, V
Drain current, I
Feedback pin voltage, V
Figure 26. Different Startup Scenarios of the
Output waveforms with a large enough V
Output waveforms with too small of a V
Circuits with Different V
D
CC
CC
t
startup
voltage swing can be higher due to
CC
FB
and ground pins of the product
CC(off)
CC
CC
Capacitors
so that all possible
to go below V
Desired level of V
CC
CC
capacitor be as
CC
capacitor
capacitor
time
time
time
V
V
CC
out
V
V
9.1 V
CC(off)
out
CC
V
time
time
skip
out
CC