SC122

11

5×f

osc

. Any inductor with these properties should provide

satisfactory performance.

The following table lists the manufacturers of recom-

mended inductor options.

Manufacturer/

Part #

Value

(μH)

DCR

(mΩ)

Rated

Current

(mA)

Tolerance

(%)

Dimensions

L×W×H

(mm)

Sumida 5508472xxxx

4.7

3800

90

2/5/10/20

2.2 × 1.4 × 1.6

Murata

LQM31PN4R7M00L

4.7

300

700

20

3.2 × 1.6 × 0.85

Capacitor Selection

Low ESR capacitors such as X5R or X7R type ceramic

capacitors are recommended for input bypassing and

output filtering. Low-ESR tantalum capacitors are not rec-

ommended due to possible reduction in capacitance seen

at the switching frequency of the SC122. Ceramic capaci-

tors of type Y5V are not recommended as their tempera-

ture coefficients make them unsuitable for this

application.

The input and output each require a minimum capaci-

tance value of 10μF at the programmed output voltage.

This must be considered when choosing small package

size capacitors as the DC bias must be included in their

derating to ensure this required value. For example, a

10μF 0805 capacitor may provide sufficient capacitance at

low output voltages but may be too low at higher output

voltages. Therefore, a higher nominal capacitance value

may be required to provide the minimum of 10μF at these

higher output voltages. Additional output capacitance

can be used extend the time between bursts, or to improve

load transient response. The following table lists recom-

mended capacitors.

Manufacturer/

Part Number

Value

(μF)

Rated Voltage

(VDC)

Type

Case

Size

Murata

GRM21BR60J226ME39B

22

6.3

X5R

0805

Murata

GRM31CR71A226KE15L

22

10

X7R

1206

PCB Layout Considerations

Good layout can enhance the performance of the DC-DC

converter and can avoid EMI problems, ground bounce,

and resistive voltage losses. The recommended layout is

shown in Figure 2.

The following simple design rules can be implemented to

ensure good layout:

Place the inductor and filter capacitors as close

to the device as possible and use short wide

traces between the power components.

Maximize ground metal on the component side

to improve the return connection and thermal

dissipation. Separation between the LX node

and GND should be maintained to avoid cou-

pling capacitance between the LX node and the

ground plane.

Use a ground plane with several vias connecting

to the component side ground to further reduce

noise interference on sensitive circuit nodes.

•

•

•

Applications Information (continued)

GND

SC122

GND

EN

IN

LX

OUT

GND

6.7mm

5.2mm

Figure 2 — Recommended Layout