STLD41

Selection of external components

Doc ID 022283 Rev 5

9/19

7

Selection of external components

7.1

It is recommended to use 10 µF as the input capacitor to achieve good stability of the device

7.2

It is recommended to use 2.2 µF as the optimal value of output capacitor to achieve the best

compromise between output voltage ripple and load transient response. The output ripple

can be checked using the equation for step-up architecture:

Equation 1

7.3

Inductor selection

A thin shielded inductor with a low DC series winding resistance is recommended for this

application. To achieve good efficiency in step-up mode, it is recommended to use an

resistance of the LED [

Ω, Ω, 1].

For nominal operation, the peak inductor current can be calculated using this formula:

Equation 2

where:

n

= Efficiency of the STLD41

= Input voltage at the VBAT-pin

L

= Inductance value of the inductor

f

= Switching frequency

For optimal performance of the STLD41 device, is recommended to use an inductor value of

47 µH or higher with low serial resistance and relevant saturation current calculated from the

equation above.

()

[]

Hz

,

F

,

V

,

A

;

V

f

V

C

100

*

V

V

I

V

2

OUT

OUT

)

MIN

(

IN

OUT

)

MAX

(

OUT

PK

PK

∗

∗

−

∗

=

−

()

IN

OUT

2

OUT

2

IN

IN

OUT

OUT

PEAK

V

V

V

f

L

2

V

V

V

n

I

I

∗

∗

∗

∗

∗

−

+

=