AN937

Power supply, UVLO and voltage reference

Doc ID 5655 Rev 15

13/29

where Dmax is 0.95, Css is in

μF and Ich is in μA. Soft-start time (t2) versus output voltage

and Css is shown in Figure 17.

Thanks to the voltage feed forward, the start-up time (t2) is not affected by the input voltage.

Figure 18 shows the output voltage start-up using different soft-start capacitance values:

It is mandatory a minimum capacitor value of 22 nF. The pin 2 cannot be left open.

Figure 17.

Soft-start time (t2) vs Vo and Css

Figure 18.

Output rising voltage with Css 56 nF, 100 nF, 22 0nF

0

3

6

9

12 15 18 21 24

0

10

20

30

40

50

60

70

(ms)

1

μF

470nF

330nF

220nF

100nF

D97IN687