ACT8309/8310/8311

Rev 1, 15-Nov-12

Innovative Power

TM

- 7 -

www.active-semi.com

Copyright © 2012 Active-Semi, Inc.

a logic-level “Power-OK” signal, simply connect a pull-

up resistor from POK to an appropriate output volt-

age.

PCB Layout Considerations

High switching frequencies and large peak current

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 volt-

age gradients in the ground plane, both of which can

result in instability or regulation errors. Step-down

DC/DCs exhibit discontinuous input current, so the

input capacitors should be placed as close as possi-

ble 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 con-

figuration, and this point should be connected to the

backside ground plane with multiple vias. For fixed

output voltage options the output node for each regu-

lator should be connected to its corresponding FB pin

through the shortest possible route, while keeping

sufficient distance from switching nodes to prevent

noise injection. Adjustable output versions should

follow the same guidelines, but additionally connect

the feedback resistors to the FB pin as close to the

IC as possible to minimize noise injection.