ACT5830 datasheet(18/41 Pages) ACTIVE-SEMI

18 / 41 page

STEP-DOWN DC/DC CONVERTER

ACT5830

Rev PrB, 05-Mar-08

Innovative Power

- 18 -

www.active-semi.com

ActivePMU

TM is a trademark of Active-Semi.

2CTM is a trademark of Philips Electronics.

FUNCTIONAL DESCRIPTIONS CONT’D

Inductor Selection

REG utilizes current-mode control and a proprietary

internal compensation scheme to simultaneously

simplify external component selection and optimize

transient performance over its full operating range.

REG was optimized for operation with a 3.3µH in-

ductor, although inductors in the 2.2µH to 4.7µH

range can be used. Choose an inductor with a low

DC-resistance, and avoid inductor saturation by

choosing inductors with DC ratings that exceed the

maximum output current of the application by at least

30%.

PCB Layout Considerations

High switching frequencies and large peak currents

make PC board layout an important part of step-

down DC/DC converter design. A good design mini-

mizes excessive EMI on the feedback paths and

voltage gradients in the ground plane, both of which

can result in instability or regulation errors. Step-

down DC/DC exhibits discontinuous input current,

so the input capacitors should be placed as close

as possible to the IC, and avoiding the use of vias if

possible. The inductor, input filter capacitor, and

output filter capacitor should be connected as close

together as possible, with short, direct, and wide

traces. The ground nodes for each regulator's

power loop should be connected at a single point in

a star-ground configuration, and this point should

be connected to the backside ground plane with

multiple vias. The output node should be connected

to the VBUCK pin through the shortest possible

route, while keeping sufficient distance from switch-

ing nodes to prevent noise injection. Finally, the

exposed pad should be directly connected to the

backside ground plane using multiple vias to

achieve low electrical and thermal resistance.

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