The internal soft-start circuitry controls the output voltage slope during startup. This avoids excessive inrush current and ensures a controlled output voltage rise time. It also prevents unwanted voltage drops from high impedance power sources or batteries. When EN is set high to start operation, the device starts switching after a delay of about 200 μs then the internal reference and hence VOUT rises with a slope controlled by an external capacitor connected to the SS/TR pin.

Leaving SS/TR pin unconnected provides fastest startup ramp with 150 µs typically.

If the device is set to shutdown (EN = GND), undervoltage lockout or thermal shutdown, an internal resistor pulls the SS/TR pin down to ensure a proper low level. Returning from those states causes a new startup sequence as set by the SS/TR connection.

A voltage supplied to SS/TR can be used to track a master voltage. The output voltage follows this voltage in both directions up and down in forced PWM mode. In PFM mode, the output voltage decreases based on the load current. The SS/TR pin of several devices must not be connected with each other.