ACT8796
Rev1, 10-Oct-08
LOW-DROPOUT LINEAR REGULATORS
FUNCTIONAL DESCRIPTION (CONT’D)
PCB Layout Considerations
PCB Layout Considerations The ACT8796’s LDOs
provide good DC, AC, and noise performance over
a wide range of operating conditions, and are rela-
tively insensitive to layout considerations. When
designing a PCB, however, careful layout is neces-
sary 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 regu-
lators to prevent noise-coupling through ground.
Output traces should be routed to avoid close prox-
imity to noisy nodes, particularly the SW nodes of
the DC/DCs.
REFBP is a filtered reference noise, and internally
has a direct connection to the linear regulator con-
troller. Any noise injected onto REFBP will directly
affect the outputs of the linear regulators, and there-
fore 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 ca-
pacitor should be placed as close to the IC as pos-
sible, 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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