ACE752D

120KHz 3.5A Buck DC-DC Converter

VER 1.1

5

APPLICATIONS INFORMATION

Output Voltage and Feedback Loop Settings

Refer to the figure 1, the output voltage of the switching regulator (VOUT) can be set with Equation

following:

)X0.835V

The limit current is set by the external resistor R2:

The ACE752D uses a patent-pending output voltage compensation scheme for the conductor wire loss

by properly selecting the value of R3, R4, if the conductor resistance is Rline, current sense resistor is R2

(Refer to the figure1), then:

R3 =

R4 =

For Rline=70mΩ, R2=33.3mΩ (2.1A current limit as figure 1), VOUT=5V:

R3=11k, R4=2.2k, choose R3=10k, R4=2k as the figure1.

Component Selection

Inductor Selection

The ACE752D can utilize small inductors due to its fast 120kHz switching frequency. Typically, a 100µH

inductor is recommended for most applications. Larger values of inductance will allow greater output

current capability by reducing the inductor ripple current. Increasing the inductance above will also

increase size.

The inductor current ripple is typically set for 20% to 40% of the maximum inductor current (IP). The

inductor should have low DCR (series resistance of the windings) to reduce the power losses, and must

be able to handle the peak inductor current without saturating. To minimize radiated noise, use a shielded

bobbin inductor.

Output and Input Capacitor Selection

Low ESR (equivalent series resistance) capacitors should be used to minimize the output voltage ripple.

The parallel of multilayer ceramic and electrolytic capacitors is an excellent choice as they have extremely

low ESR and are low cost.

A parallel of 10µF ceramic capacitor and 220µF electrolytic capacitor is sufficient for most applications.

Larger values may be used to obtain extremely low output voltage ripple and improve transient response.

Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the

battery. It follows that ceramic capacitors are also a good choice for input decoupling, and should be

located as close as possible to the device. A 10µF input capacitor is sufficient for virtually any application.

For all the ceramic capacitors above, X5R and X7R dielectric materials are preferred, for their ability to

maintain capacitance over wide voltage and temperature ranges.

R3

R4

70mV

R2

Rline

200

μ*R2

0.835*R3