NCP1562B ON Semiconductor, NCP1562B Datasheet - Page 16

• Manufacturer Part Number: NCP1562B
• Description: High Performance Active Clamp/Reset PWM Controller
• Manufacturer: ON Semiconductor

immediately discharged and the outputs are disabled. V
should not be pulled up or down externally.
CURRENT LIMIT
cycle−by−cycle and cycle skip, providing the best
protection during momentary and continuous overcurrent
conditions.
Cycle−by−Cycle
voltage on the CS pin reaches the current limit voltage
threshold (V
and the NCP1562B has a V
V
If the voltage on the V
The
In cycle−by−cycle, the conduction period ends once the
V
CSKIP(valley)
CSKIP(peak)
Figure 36. Soft−Stop Behavior After Soft−Start
V
V
V
EA
SS
CSKIP
V
NCP1562
V
ILIM
CS
SS
ILIM
is Complete and V
(V
). The NCP1562A has a V
EA
is not controlling the duty cycle)
has
AUX
ILIM
pin reaches V
two
of 0.5 V.
EA
FF Ramp
overcurrent
is Open.
AUX(off2)
Figure 37. Cycle Skip Waveforms
ILIM
of 0.2 V
, C
modes,
http://onsemi.com
SS
SS
is
16
Cycle Skip
been used to trigger a cycle skip fault. Unfortunately, the
fast response time of modern controllers makes it hard to
reach a voltage on the CS pin higher than V
cycle skip fault, the NCP1562 uses a timer. It monitors the
current
cycle−by−cycle current limit condition exists the converter
is disabled. The time to disable the converter and the time
the converter is disabled are programmed by the capacitor
on the CSKIP pin, C
continuous 100 mA current once cycle−by−cycle current
limit fault is detected. If the current limit fault persists,
C
upper threshold (V
converter enters the soft–stop mode and C
discharged with a constant 10 mA current. A new soft−start
sequence commences once C
skip threshold (V
condition is still present, the capacitor starts charging on
the next current limit event. Otherwise, C
discharged down to 0 V.
remembering previous overcurrent conditions. If a
continuous overcurrent condition is removed before
reaching
discharge. If the continuous overcurrent fault is once again
detected before C
charges from its existing voltage level, taking less time to
reach V
during a continuous overcurrent condition. For optimal
operation, the cycle skip discharge time should be longer
than the soft−stop period.
CSKIP
Traditionally, a voltage on the CS higher than V
Instead of using a higher voltage threshold to detect a
The cycle skip detection circuit charges C
The cycle skip capacitor provides a means of
CSKIP(peak)
continues to charge until reaching the cycle skip
limit
V
CSKIP(peak)
CSKIP(valley)
comparator
CSKIP
. Figure 37 shows operating waveforms
CSKIP(peak)
CSKIP
, C
is completely discharged, C
.
CSKIP
CSKIP
) of 0.5 V. If the overcurrent
) of 3.0 V. Once reached, the
and
reaches the lower cycle
starts a
if
a
ILIM
CSKIP
continuous
controlled
.
CSKIP
CSKIP
ILIM
with a
CSKIP
has
is
is