AN937 Datasheet, PDF (13/29 Pages) STMicroelectronics – The L4971 is a 1.5 A monolithic dc-dc converter

AN937
Power supply, UVLO and voltage reference
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
t_ss
(ms)
70
60
D97IN687
1μF
50
40
470nF
30
330nF
20
220nF
10
100nF
0
0 3 6 9 12 15 18 21 24 V_O(V)
Figure 18. Output rising voltage with Css 56 nF, 100 nF, 22 0nF
Doc ID 5655 Rev 15
13/29