参数资料
| 型号： | NCP1282BDR2G |
| 厂商： | ON Semiconductor |
| 文件页数： | 15/22页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST FLYBK VM 16SOIC |
| 标准包装： | 1 |
| PWM 型： | 电压模式 |
| 输出数： | 2 |
| 频率 - 最大： | 1MHz |
| 占空比： | 85% |
| 电源电压： | 8.5 V ~ 20 V |
| 降压： | 无 |
| 升压： | 是 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 16-SOIC（0.154"，3.90mm 宽） |
| 包装： | 剪切带 (CT) |
| 其它名称： | NCP1282BDR2GOSCT |
NCP1282
Cycle Skip
(V EA is not controlling the duty cycle)
Traditionally, a voltage on the CS higher than V ILIM has
been used to trigger a cycle skip fault. Unfortunately, the
V EA
V SS
FF Ramp
fast response time of modern controllers makes it hard to
reach a voltage on the CS pin higher than V ILIM .
Instead of using a higher voltage threshold to detect a
cycle skip fault, the NCP1282 uses a timer. It monitors the
current limit comparator and if a continuous
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 CSKIP .
The cycle skip detection circuit charges C CSKIP with a
continuous 100 m A current once cycle-- by-- cycle current
limit fault is detected. If the current limit fault persists,
Figure 36. Soft--Stop Behavior After Soft--Start
is Complete and V EA is Open.
If the voltage on the V AUX pin reaches V AUX(off2) , C SS is
immediately discharged and the outputs are disabled. V SS
should not be pulled up or down externally.
CURRENT LIMIT
The NCP1282 has two overcurrent modes,
cycle-- by-- cycle and cycle skip, providing the best
protection during momentary and continuous overcurrent
conditions.
Cycle--by--Cycle
In cycle-- by-- cycle, the conduction period ends once the
voltage on the CS pin reaches the current limit voltage
threshold (V ILIM ). The NCP1282 has a V ILIM of 0.5 V.
C CSKIP continues to charge until reaching the cycle skip
upper threshold (V CSKIP(peak) ) of 3.0 V. Once reached, the
converter enters the soft–stop mode and C CSKIP is
discharged with a constant 10 m A current. A new soft-- start
sequence commences once C CSKIP reaches the lower cycle
skip threshold (V CSKIP(valley) ) of 0.5 V. If the overcurrent
condition is still present, the capacitor starts charging on
the next current limit event. Otherwise, C CSKIP is
discharged down to 0 V.
The cycle skip capacitor provides a means of
remembering previous overcurrent conditions. If a
continuous overcurrent condition is removed before
reaching V CSKIP(peak) , C CSKIP starts a controlled
discharge. If the continuous overcurrent fault is once again
detected before C CSKIP is completely discharged, C CSKIP
charges from its existing voltage level, taking less time to
reach V CSKIP(peak) . Figure 37 shows operating waveforms
during a continuous overcurrent condition. For optimal
operation, the cycle skip discharge time should be longer
than the soft-- stop period.
V ILIM
CS
V CSKIP(peak)
V CSKIP
V CSKIP(valley)
V SS
Figure 37. Cycle Skip Waveforms
In some instances it may be desired to latch (instead of auto
re--start) the NCP1282 after a cycle skip event is detected.
This can be easily achieved by adding an external latch.
Figures 35 and 36 show an implementation of an integrated
and a discrete latch, respectively. In general the circuits work
by pulling CSKIP to V REF , preventing it from reaching
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