MAX1777/MAX1977/MAX1999
High-Efficiency, Quad Output, Main Power-
Supply Controllers for Notebook Computers
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4) Make the DC-DC controller ground connections as
follows: near the device, create a small analog
ground plane. Connect the small analog ground
plane to GND (Figure 13) and use the plane for the
ground connection for the REF and V
CC
bypass
capacitors, FB dividers, and ILIM resistors (if any).
Create another small ground island for PGND, and
use the plane for the V+ bypass capacitor, placed
very close to the device. Connect the AGND and
PGND planes together at the GND pin of the device.
5) On the board’s top side (power planes), make a
star ground to minimize crosstalk between the two
sides. The top-side star ground is a star connection
of the input capacitors and synchronous rectifiers.
Keep the resistance low between the star ground
and the source of the synchronous rectifiers for
accurate current limit. Connect the top-side star
ground (used for MOSFET, input, and output
capacitors) to the small island with a single short,
wide connection (preferably just a via).
Create PGND islands on the layer just below the
top-side layer (refer to the MAX1777 EV kit for an
example) to act as an EMI shield if multiple layers
are available (highly recommended). Connect each
of these individually to the star ground via, which
connects the top side to the PGND plane. Add one
more solid ground plane under the device to act as
an additional shield, and also connect the solid
ground plane to the star ground via.
6) Connect the output power planes (V
CORE
and system
ground planes) directly to the output filter capacitor
positive and negative terminals with multiple vias.
