Selecting components for your applications

AN2728

10/20

The peak current through the inductor is given by:

Equation 7

It can be observed that if the inductor value decreases, the peak current (that has to be

lower than the current limit of the device) increases. So, for fixed peak current protection,

higher value of the inductor permits a higher value of the output current.

2.5

Layout considerations

Due to the high switching frequency and peak current, the layout is an important design step

for all switching power supplies. If the layout is not carefully done, important parameters

such as efficiency and output voltage ripple could be compromised.

Short, wide traces must be implemented for main current and for power ground paths as

shown in bold in Figure 10. The input capacitor must be placed as close as possible to the

device pins as well as the inductor and output capacitor.

A common ground node minimizes ground noise, as shown in Figure 10.

2

I

I

OUT

PK

∆ I

+

=

2

I

I

OUT

PK

∆ I

+

=

Figure 10.

Layout considerations

V

IN

V

FB

SW

GND

V

IN

V

OUT

2

3

EN

1

5

4

ST1S12_ADJ

L1

R

1

C2

R

2

C1

GND

V

IN

V

FB

SW

GND

V

IN

V

OUT

2

3

EN

1

5

4

ST1S12_ADJ

L1

R

1

C2

R

2

C1

GND