Typical application

AN938

20/33

Doc ID 5410 Rev 10

over the input / output voltage range.

3.5

Output capacitors

The output capacitors selection, Co, is mainly driven by the output ripple voltage that has to

be guaranteed, in this case 1% max. of Vo.

The output ripple is defined by the ESR of Co and by the ripple current flowing through it.

The chosen total capacitance is 2 x 150 µF/35 V KY (Nippon Chemi-con), each of which has

an ESR of 150 m

Ω at 20°C. The ideal ripple voltage over the input voltage range is shown in

Figure 28.

Figure 28.

kHz)

Figure 26.

Ideal inductor value requested for

30% ripple current, as a function of

max. input voltage and output

Figure 27.

Ideal inductor value requested for

30% ripple current, as a function of

max. input voltage and output

AM03510v1

10

15

20

25

30

354045

10

15

20

25

30

35

40

45

50

55

60

Vout = 1.5 V

Vout = 2.5 V

Vout = 3.3 V

Vout = 5 V

Vout = 12 V

51 mV

Vin