参数资料
| 型号： | NCP1282BDR2G |
| 厂商： | ON Semiconductor |
| 文件页数： | 14/22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
DETAILED OPERATING DESCRIPTION
The NCP1282 is a voltage mode controller designed for
ac-- dc or dc-- dc converters requiring high-- efficiency and
low parts count. This controller incorporates two in phase
outputs with an adjustable overlap delay. The main output
is designed for driving a forward converter primary
MOSFET. The secondary output is designed for driving an
active clamp circuit MOSFET, a synchronous rectifier on
the secondary side, or an asymmetric half bridge circuit.
Two distinctive features of the NCP1282 are the
soft-- stop and a cycle skip overcurrent detector with a time
threshold. The soft-- stop powers down the converter in a
controlled manner after a fault is detected. The cycle skip
timer disables the converter if a continuous overcurrent
condition is present.
The NCP1282 reduces component count and system size
by incorporating high accuracy on critical specifications
such as programmable maximum duty cycle, undervoltage
detector and overcurrent threshold. A minimum operating
voltage of 8.5 V ensures enough voltage is available for
driving high voltage MOSFETs. Additional features found
in the NCP1282 include line feedforward, bidirectional
frequency synchronization up to 1.0 MHz, cycle-- by-- cycle
current limit with leading edge blanking (LEB),
independent under and overvoltage detectors, internal
startup circuit and soft-- start.
Once the converter enters the soft-- stop mode, it will stay
in soft-- stop mode until V SS reaches 0.2 V even if the fault
is removed prior to reaching 0.2 V.
Depending on the converter state, a soft-- stop sequence
is handled differently to ensure the fastest response time
and prevent system malfunction. If a soft-- stop sequence
starts before V SS exceeds the maximum voltage clamp of
the FF Ramp (typ. 3.0 V) and the PWM Comparator (V EA )
is not yet controlling the duty cycle, a controlled discharge
of C SS commences immediately, as shown in Figure 34.
However, if V EA is controlling the duty cycle, C SS is
discharged until soft-- stop sets a duty cycle equal to the duty
cycle set by V EA . A controlled discharge commences
afterwards, as shown in Figure 35. If V SS exceeds the FF
Ramp and the V EA is not controlling the duty cycle, V SS is
forced to the peak voltage of the FF Ramp, before starting
a controlled discharge of C SS , as shown in Figure 36. The
duty cycle set at the beginning of the soft-- stop event never
exceeds the duty cycle prior to the soft-- stop event.
(V EA is not controlling the duty cycle)
V EA
SOFT--STOP AND SOFT--START
The NCP1282 incorporates a novel soft-- stop and
soft-- start architecture that combines soft-- start and
soft-- stop functions on a single pin.
Soft-- stop reduces the duty cycle until it reaches 0% once
a fault is detected. By slowly reducing the duty cycle during
power down, the active clamp capacitor (C clamp ) is
discharged. This prevents oscillations between the power
V SS
FF Ramp
transformer and C clamp , and ensures the converter turns off
in a predictable state.
Soft-- start slowly increases the duty cycle during power
up allowing the controller to gradually reach steady state
operation. Combined, both features reduce system stress
and power surges.
The duty cycle is controlled by comparing the SS
Figure 34. Soft--Stop Before Soft--Start
is Complete and V EA is Open.
capacitor voltage (V SS ) to the Feedforward (FF) Ramp.
Soft-- start or soft-- stop is implemented by slowly charging
or discharging the capacitor on the SS pin. OUT1 is
disabled once the FF Ramp exceeds V SS . The soft-- start
charge current is 20 m A and the soft-- stop discharge current
is 100 m A, guaranteeing a faster turn OFF time.
The preset 1:5 charge:discharge ratio can be reduced by
placing an external resistor between the V REF and SS pins.
The resistor should be sized such that the total charge
current does not exceed 100 m A. Otherwise, the converter
V SS
V EA
V X = V EA -- V f
will not be able to complete a soft-- stop sequence.
The converter enters a soft-- stop sequence if an
undervoltage, overvoltage, cycle skip low V AUX
(V AUX(off1) ) or thermal shutdown condition is detected.
Figure 35. Soft--Stop Behavior when V EA Controls
the Duty Cycle.
http://onsemi.com
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