ACT8309/8310/8311
a logic-level “Power-OK” signal, simply connect a pull-
up resistor from POK to an appropriate output volt-
age.
Rev 1, 15-Nov-12
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.
Innovative Power
TM
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