Application information

STLED25

20/30

Doc ID 022323 Rev 3

7

Application information

7.1

External passive components

7.1.1

Inductor selection

The inductor is the key passive component for switching converters.

For the STLED25, an inductance of 4.7 µH is recommended. It is very important to select

the right inductor according to the maximum current the inductor can handle to avoid

saturation. The peak current for the step-up can be calculated with the following formula:

Equation 2

where:

maximum among VD1-D5

fs: switching frequency. Use the minimum value of 2.25 MHz for the worst case

η: efficiency of step-up converter. It is 0.87 at 75 mA load

7.1.2

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 maintain stable operation of the

L

fs

V

2

)

VIN

V

(

VIN

VIN

I

V

I

OUT

MIN

OUT

MIN

MIN

OUT

OUT

BOOST

PEAK

×

×

×

−

×

+

×

η

×

=

−

Table 7.

List of recommended inductors

Manufacturer

Part number

Inductance

[µH]

Saturation current [A]

Size [mm]

Samsung

CIG21K4R7SCE

4.7

0.6

0805

Murata

LQM21PN4R7

4.7

0.6

0805