NCP1075(2012) Ver la hoja de datos (PDF) - ON Semiconductor
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NCP1075 Datasheet PDF : 26 Pages
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NCP1072, NCP1075
Improving the precision in auto−recovery OVP
Given the OVP variations the internal trip current
dispersion incur, it is sometimes more interesting to explore
a different solution, improving the situation to the cost of a
minimal amount of surrounding elements. Figure 27 shows
that adding a simple zener diode on top of the limiting
resistor, offers a better precision since what matters now is
the internal 8.4 V VCC breakdown plus the zener voltage. A
resistor in series with the zener diodes keeps the maximum
current in the VCC pin below the maximum rating of 15 mA
just before trip the OVP.
Soft−Start
The NCP107X features a 1 ms soft−start which reduces
the power−on stress but also contributes to lower the output
overshoot. Figure 28 shows a typical operating waveform.
The NCP107X features a novel patented structure which
offers a better soft−start ramp, almost ignoring the start−up
pedestal inherent to traditional current−mode supplies:
Vcc
D1
Rlimit
Laux
Ground
Figure 27. A Simple Zener Diode Added in Parallel
VCCON
Drain current
Figure 28. The 1 ms soft−start sequence
Jittering
Frequency jittering is a method used to soften the EMI
signature by spreading the energy in the vicinity of the main
switching component. The NCP107X offers a ±6%
deviation of the nominal switching frequency. The sweep
sawtooth is internally generated and modulates the clock up
and down with a fixed frequency of 300 Hz. Figure 29
shows the relationship between the jitter ramp and the
frequency deviation. It is not possible to externally disable
the jitter.
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