SLUSD37E October 2017 – November 2019 UCC28056
During Stopb state operation, an internal resistor (RCODisch) is connected between the COMP and GND pins to discharge the external compensation network. Start-up transitions through the BstOffb state and switching commence only after the COMP pin voltage rises above the VBstRise threshold. Switching therefore always starts with the power demand at 12.5% of its maximum value. The Soft-ON feature ensures that the on-time period ramps up over the first four switching cycles to the demanded value. These features limit audible noise at start-up.
Because the controller enables the error amplifier fast transient gain a startup, the input power ramps to maximum at a rate limited only by the time constant of the external compensation network. This condition ensures that the output capacitance charges rapidly to limit start-up delay.