Application information

STBB3J

18/25

DocID025263 Rev 5

Equation 2

Equation 3

current. The amplitude of the inductor ripple current is typically set between 20% and 40%

of the maximum inductor current. To guarantee an inductor ripple current always lower than

the selected value

chosen.

In addition to the inductance value, also the maximum current which the inductor can handle

must be calculated in order to avoid saturation.

Equation 4

Equation 5

where

η is the estimated efficiency. The maximum of the two values above must be

considered when selecting the inductor.

8.3

Input and output capacitor selection

It is recommended to use ceramic capacitors with low ESR as input and output capacitors in

order to filter any disturbance present in the input line and to obtain stable operation.

behavior of the device. The input capacitor must be placed as close as possible to the

device.

An R-C filter is added to VINA pin (R3-C5 Figure 26) to assure a clean input voltage to the

internal logic block.

L

MIN_BUCK

V

OUT

V

IN_MAX

V

OUT

–

()

×

V

IN_MAX

f

S

ΔI

L

×

×

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

=

L

MIN_BOOST

V

IN_MIN

V

OUT

V

IN_MIN

–

()

×

V

OUT

f

S

ΔI

L

×

×

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

=

I

PEAK_BUCK

I

OUT

η

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

V

OUT

V

IN_MAX

V

OUT

–

()

×

2V

IN_MAX

f

S

L

×

×

×

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

+

=

I

PEAK_BOOST

V

OUT

I

OUT

×

η V

IN_MIN

×

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



V

OUT

V

IN_MIN

–

()

×

2V

OUT

f

S

L

×

×

×

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

+

=