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Axelite Confidential Materials, do not copy or distribute without written consent.

Rev.2.1 Oct.04, 2019

AX3050/A

Input Capacitor

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 100μF. 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. Especially C8 capacitor should be placed as

close as possible to the IC pin.

Output Capacitor

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

The output ripple voltage is:

OUT

2

LX

IN

ESR

RIPPLE

OUTMAX

RIPPLE

LC

f

×

28

V

+

R

K

I

=

V

where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is

the ESR of the output capacitor, fLX 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 type. 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 capacitor, typically choose a capacitance of about 470μF. For

tantalum or electrolytic capacitors, choose a capacitor with less than 50mΩ ESR.