400EADBA0 datasheet(29/47 Pages) ONSEMI

29 / 47 page

NCP12400

www.onsemi.com

Figure 56. Start−up, Shut−down and AC Line Unplug Time Diagram

time

VHV

time

One Shot

time

DRV

VHV(start)

tDET

time

VCC

VCC(on)

VCC(off)

VCC(inhibit)

VFB

VOFF

VON

Low consumption mode

Ready to RUN

DRV start

condition

DSS start to

charge the Vcc

cap

timer

starts

timer

restarts

AC line Unplug

detector starts

RUN

AC line unplug

X2 capacitor

discharge

Starts

only at

VCC(on)

VCC(dis)

tDIS

X2 cyclic discharge

process starts

tDET

No AC detection

X2 capacitor

discharge

tDIS

No AC detection

Low consumption off mode

Skip mode

tGTSG

Dynamic

Self−Supply

in off mode

time

Oscillator with Frequency Jittering

The NCP12400 includes an oscillator that sets the

switching frequency 65 kHz or 100 kHz depending on the

version. The maximum duty−ratio of the DRV pin is 80%.

In order to improve the EMI signature, the switching

frequency jitters

±4 kHz around its nominal value, with a

triangle−wave shape and at a frequency of 125 Hz. This

frequency jittering is active even when the frequency is

decreased to improve the efficiency in light load condition.

Figure 57. Frequency Modulation of the Maximum

Switching Frequency

Time

fOSC

8 ms

(125 Hz)

Nominal fOSC

fOSC

+ 4 kHz

− 4 kHz

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