8.3.2 Soft Start

Each of the three converters has an internal soft-start circuit that limits the inrush current during start-up. The soft start is realized by using a low initial current to charge the internal compensation capacitor. The soft-start time is typically 750 μs if the output voltage ramps from 5% to 95% of the final target value. If the output is already precharged to some voltage when the converter is enabled, then this time is reduced proportionally. There is a short delay of typically 170 μs between the converter being enabled and switching activity actually starting. This allows the converter to bias itself properly, to recognize if the output is precharged, and if so to prevent discharging of the output while the internal soft-start ramp catches up with the output voltage.