SCY99080CDWR2G 데이터 시트보기 (PDF) - ON Semiconductor

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SCY99080CDWR2G

High Performance Switch-Mode Power Supply Controller for Backlight and LLC Converters

ON Semiconductor 

DDA002C

VDD

CIG _I = 10 uA

CIG

to VCO

CPREHEAT

CIG_ E = 5 V

to Soft −Start

discharge

100ms PFC

PFC_OK

timer

BO OK

Vcc Reset

Figure 42. CIG Timer Internal Connection

The preheat time can be easily calculated using Equation 1:

Where:

TCIG + CPreheat @ 0.5

(eq. 1)

TCIG

is the preheat period time in seconds

CPreheat

is the preheat capacitor value in mF

Note that the PFC delay period takes place prior to preheat

period. Soft−start period starts immediately after the preheat

capacitor voltage is higher than 5 V. If using this IC to drive

a resonant SMPS or another application that does not require

preheating, use 100 nF capacitor on the CIG pin to overcome

false triggering by external noise.

Soft−start Sequence

In resonant converters, a soft−start is needed to avoid

suddenly applying the full current into the resonant tank.

The soft−start is fully controlled by the external component

values when using DDA002C controller − refer to

Figure 43.

Rfmin

R_Fmin

Rfstart

SS

CSS

SS_E = 1.9 V

FB timer

enable

CIG_END

from CIG

block

Figure 43. Soft−start Block Internal Connection

The soft−start capacitor is discharged by an internal

switch before the soft−start period begins. The discharging

path is released at the end of the CIG period. The switching

frequency is then given by the parallel combination of

resistors Rfmin and Rfstart. Since the soft−start capacitor

charges from the R_Fmin reference voltage, via the Rfstart

resistor, the current driven from the R_Fmin pin

exponentially decreases, as does the switching frequency. In

case the feedback path does not take control, the switching

frequency will reach a value that is given by the Rfmin

resistor. The feedback fault timer is disabled during the PFC

delay, preheat, and soft−start periods in order to overcome

unwanted controller operation interruption. This is

accomplished by an internal comparator that monitors the

soft−start capacitor voltage. The feedback fault timer is

enabled when the soft−start capacitor voltage reaches 1.9 V.

Please note that the soft−start sequence is activated after any

controller restart. The PFC delay and preheat periods always

precede the soft start action. The typical startup sequence of

the DDA002C can be seen in Figure 44.

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