NCP1250ASN100T1G ONSEMI [ON Semiconductor], NCP1250ASN100T1G Datasheet - Page 17

• Manufacturer Part Number: NCP1250ASN100T1G
• Description: Current-Mode PWM Controller for Off-line Power Supplies
• Manufacturer: ONSEMI [ON Semiconductor]

fixes the maximum peak current set point to 0.8 V even if the
OPP pin is inadvertently biased above 0 V.
Frequency Foldback
the need for improving the efficiency, requires a change to
the traditional fixed−frequency type of operation. This
controller implements a switching frequency foldback when
the feedback voltage passes below a certain level, V
around 1.5 V. At this point, the oscillator enters frequency
Auto−Recovery Short−Circuit Protection
experiences a severe overloading situation, an internal error
flag is raised and starts a countdown timer. If the flag is
asserted longer than 100 ms, the driving pulses are stopped
and the V
point, the controller wakes−up and the V
Figure 43. By Observing the Voltage on the Feedback Pin, the Controller Reduces its Switching Frequency for an
Finally, please note that another comparator internally
The reduction of no−load standby power associated with
In case of output short−circuit or if the power supply
FB
CC
pin slowly goes down to around 7 V. At this
Frequency
65 kHz
26 kHz
F
sw
min
min
V
350 mV
fold,end
CC
Improved Performance at Light Load
builds up again
1.5 V
V
fold
fold
http://onsemi.com
max
, set
3.4 V
17
V
V
FB
FB
foldback and reduces its switching frequency. The peak
current setpoint follows the feedback pin until its level
reaches 1.05 V. Below this value, the peak current freezes to
V
and the only way to further reduce the transmitted power is
to reduce the operating frequency down to 26 kHz. This
value is reached at a voltage feedback level of 350 mV
typically. Below this point, if the output power continues to
decrease, the part enters skip cycle for the best noise−free
performance in no−load conditions. Figure 43 depicts the
adopted scheme for the part.
due to the resistive starting network. When V
VCC
absence of the fault. If the fault is still there, the supply enters
another cycle of so−called hiccup mode. If the fault has
cleared, the power supply resumes normal operation. Please
note that the soft−start is activated during each of the re−start
sequence.
fold
/4.2 (250 mV or 31% of the maximum 0.8 V setpoint)
ON
, the controller attempts to re−start, checking for the
Peak current setpoint
[
[ 0.25 V
0.36 V
0.8 V
V
CS
min
V
1.05 V
freeze
V
1.5 V
fold
3.4 V
max
V
CC
FB
reaches