DocID025723 Rev 4

19/29

ST1S50

Application information

29

6.5

Soft-start capacitor selection

6.5.1

Reset time

The soft-start capacitor allows managing the correct rising of the output voltage to prevent

a high inrush current. Moreover it introduces a reset time in case the device is disabled and

re-enabled through UVLO.

The re-enable through UVLO, after disable though UVLO, must happen after a certain reset

time to assure the proper startup. This reset time is a function of the soft-start capacitor.

A 4.7 M

 resistor value in parallel to the soft-start capacitor is strongly recommended in

order to predict the reset time.

Figure 8. Soft-start circuit

The reset time is so calculated:

Equation 24

Figure 9. Reset time



=