LSP5502

2A Synchronous Step Down DC/DC Converter

5/11

Rev. 1.7

www.liteon-semi.com

The input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the

converter. A low ESR capacitor is highly recommended. Since large current flows in and out of this capacitor during

switching, its ESR also affects efficiency.

The input capacitance needs to be higher than 10µF. The best choice is the ceramic type; however, low ESR

tantalum or electrolytic types may also be used provided that the RMS ripple current rating is higher than 50% of the

output current. The input capacitor should be placed close to the IN and G pins of the IC, with the shortest traces

possible. In the case of tantalum or electrolytic types, they can be further away if a small parallel 0.1µF ceramic

capacitor is placed right next to the IC.

Output Capacitor

The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is:

ESR

RIPPLE

OUTMAX

RIPPLE

R

K

I

V

=

OUT

LC

SW

f

IN

V

2

•

8

+

(3)

where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR of the output capacitor, fSW

is the switching frequency, L is the inductor value, and COUT is the output capacitance. In the case of ceramic output

capacitors, RESR is very small and does not contribute to the ripple. Therefore, a lower capacitance value can be

used for ceramic capacitors. In the case of tantalum or electrolytic capacitors, the ripple is dominated by RESR

multiplied by the ripple current. In that case, the output capacitor is chosen to have sufficiently low ESR.

For ceramic output capacitors, typically choose a capacitance of about 22µF. For tantalum or electrolytic capacitors,

choose a capacitor with less than 50mΩ ESR.

Optional Schottky Diode

During the transition between high-side switch and low-side switch, the body diode of the low side power MOSFET

conducts the inductor current. The forward voltage of this body diode is high. An optional Schottky diode may be

paralleled between the SW pin and GND pin to improve overall efficiency. Table 2 lists example Schottky diodes and

their Manufacturers.

Table 2-Diode Selection Guide

Part Number

Voltage/Current Rating

Vendor

B130

30V,1A

Lite-on Semiconductor Corp.

MBRS130

30V,1A

International Rectifier

VIN = 12V

LSP5502

IN

EN

FB

SW

C1

C2

0.1uF

C5

47pF

C6

10nF

R2

10k

R3

6.8k

COMP

R4

100k

BS

C4

2.2nF

2

7

3

5

1

8

6

SS

0.1uF

C3

4

22uF/16V

15uH/2A

L1

44.2k

VOUT = 5V/2A

R1

D1

B130/SK13

(Option)

GND

C7

22µF/10V

CERAMIC

x2

Free Datasheet http://www.nDatasheet.com