DocID17928 Rev 6

15/30

ST1S40

Application information

30

In Table 6 some multi layer ceramic capacitors suitable for this device are reported.

ESR and ESL are minimized, is suggested in order to prevent instability on the output

voltage due to noise. The value of the bypass capacitor can go from 330 nF to 1 µF.

6.2

Inductor selection

The inductance value fixes the current ripple flowing through the output capacitor. So the

minimum inductance value, to have the expected current ripple, must be selected. The rule

to fix the current ripple value is to have a ripple at 20% to 40% of the output current.

In continuous current mode (CCM), the inductance value can be calculated by Equation 18

Equation 18

30% of the maximum output current, the minimum inductance value can be calculated:

Equation 19

The peak current through the inductor is given by:

Equation 20

so if the inductor value decreases, the peak current (that must be lower than the current limit

of the device) increases. The higher the inductor value, the higher the average output

current that can be delivered, without reaching the current limit.

Table 6. Input MLCC capacitors

Manufacturer

Series

Cap value (

F)

Rated voltage (V)

Murata

GRM31

10

25

GRM55

10

25

TDK

C3225

10

25

I

L

V

IN

V

OUT

–

L



V

OUT

L



==

L

MIN

V

OUT

I

MAX

----------------

1D

MIN

–

F

SWMIN

-----------------------



=

I

LPK



I

O

I

L

2

--------

+

=