Data Sheet G14309EJ2V0DS00

11

µµµµPC1909

3. OPERATION OVERVIEW

3.1 Startup

The operating waveforms at startup are shown in Figure 3-1 below. The operations at startup are as follows.

<1>

When the power supply voltage (VCC) rises and exceeds the starting voltage (VCC(L to H)), the reference voltage

(VREF) rises.

<2>

The DTC1 voltage is boosted as the soft start capacitor is charged (refer to 4.5.3 Soft start).

<3>

Because the DTC1 voltage is at a lower potential than other voltages, OUT1 and OUT2 become low and high

level respectively during the T1 period.

<4>

If the DTC1 voltage is further boosted so that there is a period in which it is higher than the dCT voltage in the

T2 period, OUT2 becomes low level. In the period in which the DTC1 voltage exceeds CT, OUT1 and OUT2 are

high and low level respectively. The duty of OUT1 increases and that of OUT2 decreases as DTC1 is boosted.

Figure 3-1. Waveforms at Startup

VCC

VTH(H)

VTH(L)

OUT1

OUT2

CT

DTC1

DTC2

T1

T2

VREF

dCT

FB

VCC(LtoH)

VH

5