SNVSBT8 March 2021 TPSM13604H
PRODUCTION DATA
Programmable soft start permits the regulator to slowly ramp to its steady-state operating point after being enabled, thereby reducing current inrush from the input supply and slowing the output voltage rise-time to prevent overshoot.
Upon turn-on, after all UVLO conditions have been passed, an internal 8-µA current source begins charging the external soft-start capacitor. The soft-start time duration to reach steady-state operation is given by the formula:
Equation 4 can be rearranged as follows:
Use of a 4700-pF capacitor results in 0.5-ms soft-start duration. This is a recommended value. Note high values of CSS capacitance causes more output voltage droop when a load transient goes across the DCM-CCM boundary. Use Equation 22 to find the DCM-CCM boundary load current for the specific operating condition. If a fast load transient response is desired for steps between DCM and CCM mode, the soft-start capacitor value must be less than 0.018 µF.
Note the following conditions reset the soft-start capacitor by discharging the SS input to ground with an internal 200-μA current sink: