ACT4523AYH-T データシートの表示（PDF） - Active-Semi, Inc

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ACT4523AYH-T

Wide-Input Sensorless CC/CV Step-Down DC/DC Converter

Active-Semi, Inc 

ACT4523A

Rev 0, 25-Jul-13

APPLICATIONS INFORMATION CONT’D

For ceramic output capacitor, typically choose a

capacitance of about 22µF. For tantalum or

electrolytic capacitors, choose a capacitor with less

than 50mΩ ESR.

This diode is also recommended for high duty cycle

operation and high output voltage applications.

Rectifier Diode

Use a Schottky diode as the rectifier to conduct

current when the High-Side Power Switch is off.

The Schottky diode must have current rating higher

than the maximum output current and a reverse

voltage rating higher than the maximum input

voltage.

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

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:

VRIPPLE

= I K R OUTMAX RIPPLE ESR

+

28

VIN

× fSW 2 LCOUT

(6)

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 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.

Innovative PowerTM

-7-

www.active-semi.com

Copyright © 2013 Active-Semi, Inc.

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