®
ACT5830
Rev 2, 20-Jan-11
STEP-DOWN DC/DC CONVERTER
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
inductor, 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
minimizes 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
switching 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.
Innovative PowerTM
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