NCP1252 ON Semiconductor, NCP1252 Datasheet - Page 12

• Manufacturer Part Number: NCP1252
• Description: Flyback Applications
• Manufacturer: ON Semiconductor

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and the SS pin is internally grounded in order to discharge
the soft start capacitor connected to this pin (Case #3). If the
BO pin is released, when its level reaches the V
new soft start sequence happens.
DRV pin
V
When the BO pin is grounded, the controller is shut down
V
BO pin
SS pin
CC
CC(on)
V
pin
BO
Rse nse
Soft start
Rcomp
Figure 29. Controller Shuts Down with the Brown Out Pin
CASE #3
SS capacitor is
discharged
CS
SS
Iss
Vdd
Figure 30. Soft Start Principle
Soft Start
Status
BO
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level a
Time
Time
Time
Time
120 ms
Fixe d
Delay
LEB
12
Grand Reset
Soft Start:
the SS pin voltage divided by 4 controls the peak current
sensed on the CS pin. Thus as soon as the CS pin voltage
becomes higher than the SS pin voltage divided by 4 the
driver latch is reset.
DRV pin
V
V
BO pin
SS pin
As illustrated by the following figure, the rising voltage on
CC
CC(on)
V
1/4
pin
BO
UVLO
+
−
Clock
Soft start
S
R
Q
Q
CASE #4
DRV
Time
Time
Time
Time