ACT8332 datasheet(9/13 Pages) ACTIVE-SEMI

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ACT8332

Rev0, 14-Mar-08

STEP-DOWN DC/DC CONVERTER

Innovative Power

- 9 -

www.active-semi.com

ActivePMU

TM is a trademark of Active-Semi.

RFB1

RFB2

OUT1

ACT8332

CFF

Figure 4:

Output Voltage Programming

Finally choose CFF using the following equation:

where RFB1 = 47kΩ, use 47pF.

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 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 loops

should be connected at a single point in a star-

ground configuration, and this point should be con-

nected to the backside ground plane with multiple

vias. For fixed output voltage options, connect the

output node directly to the FB1 pin. For adjustable

output voltage options, connect the feedback resis-

tors and feed-forward capacitor to the FB1 pin

through the shortest possible route. In both cases,

the feedback path should be routed to maintain suffi-

cient distance from switching nodes to prevent noise

injection. Finally, the exposed pad should be directly

connected to the backside ground plane using multi-

ple vias to achieve low electrical and thermal resis-

tance.

(2)

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