NCP1012 データシートの表示（PDF） - ON Semiconductor

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NCP1012

Self-Supplied Monolithic Switcher for Low Standby Power Offline SMPS

ON Semiconductor 

NCP1010, NCP1011, NCP1012, NCP1013, NCP1014

Soft−Start

The NCP101X features an internal 1.0 ms soft−start

activated during the power on sequence (PON). As soon as

VCC reaches VCCOFF, the peak current is gradually

increased from nearly zero up to the maximum internal

clamping level (e.g. 350 mA). This situation lasts 1.0 ms

and further to that time period, the peak current limit is

blocked to the maximum until the supply enters regulation.

The soft−start is also activated during the over current burst

(OCP) sequence. Every restart attempt is followed by a

soft−start activation. Generally speaking, the soft−start will

be activated when VCC ramps up either from zero (fresh

power−on sequence) or 4.7 V, the latch−off voltage

occurring during OCP. Figure 22 portrays the soft−start

behavior. The time scales are purposely shifted to offer a

better zoom portion.

VCC

8.5 V

0 V (Fresh PON)

or

4.7 V (Overload)

Current

Sense

Max Ip

1.0 ms

Figure 22. Soft−Start is activated during a startup sequence or an OCP condition.

Non−Latching Shutdown

In some cases, it might be desirable to shut off the part

temporarily and authorize its restart once the default has

disappeared. This option can easily be accomplished

through a single NPN bipolar transistor wired between FB

and ground. By pulling FB below the internal skip level

(Vskip), the output pulses are disabled. As soon as FB is

relaxed, the IC resumes its operation. Figure 23 depicts the

application example.

ON/OFF

1

2

3

4

+

CVcc

8

7

5

Drain

Figure 23. A non−latching shutdown where pulses are stopped as long as the NPN is biased.

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