SLUAAT3 November 2023 TPS56837
If the external soft start capacitor Css has pre-biased voltage at start-up, the device initially discharges the external capacitor voltage to lower voltage then charge again. This discharge is intended to prevent power up without soft start when the pre-biased voltage is higher than reference voltage.
Figure 3-2 shows TPS56837 soft start waveform when external Css has pre-biased voltage. Once EN is enabled, TPS56837 begins to discharge the pre-biased Css. When the voltage of Css reaches zero, the soft start function begins and Vout ramps up smoothly.