MS1003SH･MS1004SH

Application Note Ver.2.2

SHINDENGEN ELECTRIC MFG. CO. , LTD

8/41

3.1.2 Soft start

At startup, the OCL level changes in four stages. Current flowing to the main switch also increases in stages.

The envelope curves of the current to the main switch are shaped in four steps to avoid abrupt switch

startups.

The soft start time depends on the Tss1 to Tss3 settings. The time settings are determined by the IC.

3.1.3 Bias assist

Soon after oscillation begins during startup, the voltage drops, and the oscillation may halt. To prevent this

and ensure proper startup, the bias assist function supplies energy to the Vcc pin.

Shown below is a schematic diagram of Vcc startup incorporating the bias assist function.

Steady-state

operation

Normal OCL level

Assist function

activates.

If the voltage drops below the oscillation

stop voltage, oscillation halts, and the

startup circuit must restart.

The voltage remains above the oscillation

stop voltage to ensure that oscillation

does not halt.