of top-layer copper, so that they don’t go through
vias. The resulting top-layer “sub-ground-plane” is
connected to the normal inner-layer ground plane at
the output ground terminals. This ensures that the
analog GND of the IC is sensing at the output termi-
nals of the supply, without interference from IR
drops and ground noise. Other high-current paths
should also be minimized, but focusing ruthlessly
on short ground and current-sense connections
eliminates about 90% of all PC board layout diffi-
culties. See the evaluation kit PC board layouts for
examples.
2) Place the IC and signal components. Keep the main
switching node (LX node) away from sensitive ana-
log components (current-sense traces and REF and
SS capacitors). Placing the IC and analog compo-
nents on the opposite side of the board from the
power-switching node is desirable. Important: the
IC must be no farther than 10mm from the current-
sense resistor. Keep the gate-drive traces (DH, DL,
and BST) shorter than 20mm and route them away
from CSH, CSL, REF, and SS.
3) Employ a single-point star ground where the input
ground trace, power ground (subground plane),
and normal ground plane all meet at the output
ground terminal of the supply.
MAX1652–MAX1655
High-Efficiency, PWM, Step-Down
DC-DC Controllers in 16-Pin QSOP
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