7.3.2 Soft Start (SS), Pre-biased Output

The internal soft start circuit controls the output voltage slope during startup. This avoids excessive inrush current and provides an adjustable controlled output-voltage rise time. The soft start also prevents unwanted voltage drop from high impedance power sources or batteries.

When EN is set to start device operation, the device starts switching after a delay of typically 200 µs and VOUT rises with a slope, controlled by the external capacitor which is connected to the SS/TR pin (soft start). Leaving the SS/TR pin floating or connecting to VIN provides internally set fastest startup with a soft start slope of about 80us. See Application Curves for typical startup operation.

The device can start into a pre-biased output. In this case, the device starts switching, only when the internal set point for VOUT increases above the pre-biased voltage level.