SLUSDX1 September 2020 TPS563211
This is an optional function configured by MODE pin.
If the PG function is selected, the device works with an internal soft-start time of 2 ms. If the SS function is selected, the device has the adjustable soft-start function. When the EN pin becomes high, the soft-start charge current, ISS, begins charging the capacitor, which is connected from the PG/SS pin to GND (CSS). Smooth control of the output voltage is maintained during start-up. Use Equation 11 to calculate the soft-start time.
The value of the external soft-start capacitor must not be lower than 4 nF typical to ensure good start-up behavior.
If the output capacitor is pre-biased at start-up, the device initiates switching and starts ramping up only after the internal reference voltage becomes greater than the feedback voltage. This scheme ensures that the converters ramp up smoothly into regulation point.