®
ACT8938
Rev 3, 23-Dec-11
PCB Layout Considerations
The ACT8938’s LDOs provide good DC, AC, and
noise performance over a wide range of operating
conditions, and are relatively insensitive to layout
considerations. When designing a PCB, however,
careful layout is necessary to prevent other circuitry
from degrading LDO performance.
A good design places input and output capacitors
as close to the LDO inputs and output as possible,
and utilizes a star-ground configuration for all
regulators to prevent noise-coupling through
ground. Output traces should be routed to avoid
close proximity to noisy nodes, particularly the SW
nodes of the DC/DCs.
REFBP is a noise-filtered reference, and internally
has a direct connection to the linear regulator
controller. Any noise injected into REFBP will
directly affect the outputs of the linear regulators,
and therefore special care should be taken to
ensure that no noise is injected to the outputs via
REFBP. As with the LDO output capacitors, the
REFBP bypass capacitor should be placed as close
to the IC as possible, with short, direct connections
to the star-ground. Avoid the use of via whenever
possible. Noisy nodes, such as from the DC/DCs,
should be routed as far away from REFBP as
possible.
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