ACT4530

Rev 1.0, 19-Nov-2018

- 8 -

www.active-semi.com

Copyright © 2018 Active-Semi, Inc.

APPLICATIONS INFORMATION

Inductor Selection

The inductor maintains a continuous current to the

output load. This inductor current has a ripple that is

dependent on the inductance value.

Higher inductance reduces the peak-to-peak ripple

current. The trade off for high inductance value is

the increase in inductor core size and series

resistance, and the reduction in current handling

capability. In general, select an inductance value L

based on ripple current requirement:

correspond to the peak-to-peak ripple current being

30% of the maximum load current.

With a selected inductor value the peak-to-peak

inductor current is estimated as:

The peak inductor current is estimated as:

The maximum output current is calculated as:

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 currents flow 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 a ceramic capacitor.

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. Active Semi recommends using a ceramic

capacitor in parallel with a tantalum or electrolytic.

This combination provides the EMI and noise

performance. The input capacitor must be placed

close to the IN and GND pins of the IC, with the

shortest traces possible. If using a tantalum or

electrolytic capacitor in parallel with ceramic

capacitor, the ceramic capacitor must be placed

closer to the IC.

Output Capacitor

The ACT4530 output capacitance must be split

between the left and right side of the output current

sense resistor. The left side of the current sense

resistor (CSP pin) requires a 22uF ceramic

capacitor. The right side of the current sense

resistor should contain enough capacitance to keep

the output voltage ripple below the require level.

This output capacitance should have low ESR to

keep low output voltage ripple. The output ripple

voltage is:

the combination of ESR and real capacitance.

 

small and does not contribute to the ripple.

Therefore, a lower capacitance value can be used. In

the case of tantalum or electrolytic capacitors, the

capacitor must 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. If an 330uF or 470uF electrolytic

cap or tantalum cap is used and the output voltage

ripple is dominated by ESR, add a 2.2uF ceramic in

parallel with the tantalum or electrolytic.

Rectifier Schottky 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. Further more, the low forward voltage

Schottky is preferable for high efficiency and

smoothly operation.

(1)

(2)

(3)

(4)

(5)