Recommendations on board usage

AN2603

16/23

Doc ID 13778 Rev 3

The resistors in Table 1 provide a suitable compromise in terms of current consumption and

minimum output voltage. For output voltages close to the feedback voltage, we suggest to

add a very small capacitor in parallel with R1 in the range of 10 pF. Or, as an alternative, we

suggest to increase the current in the resistor divider by decreasing the R1 and R2 value.

4.1.1

Inductor selection

Due to the high frequency (1.5 MHz) it is possible to use very small inductor values. In this

board the device was tested with inductors in the range of 1 µH to 10 µH, with very good

efficiency results (see below plot).

As the device is able to provide an operative output current of 2 A, The use of inductors

capable of managing at least 3 A is strongly recommended.

4.1.2

Capacitor selection

It is possible to use any X5R or X7R ceramic capacitor:

●

C1 = 4.7 µF (ceramic) or higher.

●

C2 = 22 µF (ceramic) or higher. It is possible to put several capacitors in parallel in

order to reduce the equivalent series resistance and improve the ripple present in the

output voltage.

4.2

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 done carefully, 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

showed in bold in Figure 13. The input capacitor must be placed as close as possible to the

device pins as well as the inductor and output capacitor.

It is very important to connect the two input pins 4 mm far from the device, it avoids noise

inside the control circuit, coming from the power switch, as shown in Figure 9.

A common ground node minimizes ground noise, as shown in Figure 13. The exposed pad

of the package must be connected to common ground node.

Figure 13.

Layout considerations

VFB

SW

VIN_A

1

5

4

3

R1

R2

L1

Vout

C2

6

C1

GND

Vin

2

GND