Figure 6. Feed-forward

5.2

Soft-start

The soft-start is essential to ensure a correct and safe start-up of the step-down converter. It avoids inrush current

surge and makes the output voltage increase monotonically. The soft-start is performed by charging an external

capacitor, connected between SS pin and ground, with a constant current (5 µA typ.). The SS voltage is used as

reference of the switching regulator and the output voltage of the converter tracks the ramp of the SS voltage.

When the SS pin voltage reaches 0.8 V level, the error amplifier switches to the internal 0.8 V ±1% reference to

regulate the output voltage.

A7987

Soft-start

DS12928 - Rev 3

page 10/36