Application information

STODD01

22/31

Doc ID 17789 Rev 2

The critical inductance values can then be obtained according to the following formulas:

for the step-down

Equation 3

and for the step-up

Equation 4

where:

ΔI

can be set at 20 % - 40 % of the output current for the step-down and can be set at 20 % -

40 % of the input current for the step-up.

The peak current of the inductor can be calculated as:

Equation 5

Equation 6

In addition to the inductance value, in order to avoid saturation, the maximum saturation

9.4

Input and output capacitor selection

It is recommended to use ceramic capacitors with X5R or X7R dielectric and low ESR as

input and output capacitors, in order to filter any disturbance present in the input line and to

obtain stable operation. The output capacitor is very important for satisfying the output

voltage ripple requirement.

can be calculated:

L

SW

MAX

_

IN

OUT

MAX

_

IN

OUT

MIN

I

F

V

)

V

V

(

V

L

Δ

×

×

−

×

=

L

SW

OUT

MIN

_

IN

OUT

MIN

_

IN

MIN

I

F

V

)

V

V

(

V

L

Δ

×

×

−

×

=

L

F

V

2

)

V

V

(

V

)

8

.

0

/

I

(

I

SW

MAX

_

IN

OUT

MAX

_

IN

OUT

OUT

DOWN

_

STEP

PEAK

×

×

×

−

×

+

=

−

L

F

V

2

)

V

V

(

V

V

I

V

I

SW

OUT

MIN

_

IN

OUT

MIN

_

IN

MIN

_

IN

OUT

OUT

UP

_

STEP

PEAK

×

×

×

−

×

+

×

η

×

=

−