Analog Devices MAX77857Q Manual page 13

Evaluates: MAX77857 (FC2QFN)
•
Place the input capacitors (C
respectively. Since the IC operates at a high switching frequency, this placement is critical for minimizing parasitic
inductance within the input and output current loops, which can cause high voltage spikes and can damage the internal
switching MOSFETs.
•
Place the inductor next to the LX bumps (as close as possible) and make the traces between the LX bumps and the
inductor short and wide to minimize PCB trace impedance. Excessive PCB impedance reduces converter efficiency.
When routing LX traces on a separate layer (as in the examples), make sure to include enough vias to minimize trace
impedance. Routing LX traces on multiple layers is recommended to further reduce trace impedance. Furthermore,
do not let LX traces take up an excessive amount of area. The voltage on this node switches very quickly and an
additional area creates more radiated emissions.
•
Route LX nodes to their corresponding bootstrap capacitor (C
reduce trace length to the IC.
•
Connect the inner PGND bumps to the low-impedance ground plane on the PCB with vias placed next to the bumps.
Do not create PGND islands, as PGND islands risk interrupting the hot loops. Connect AGND and AGND island to the
low-impedance ground plane on the PCB (the same net as PGND).
•
Keep the power traces and load connections short and wide. This is essential for high converter efficiency.
•
Do not neglect ceramic capacitor DC voltage derating. Choose capacitor values and case sizes carefully. Refer to the
Output Capacitor Selection section in the MAX77857 IC data sheet and
**LAYOUT BASED
ON 7.0A I
LIM
CONFIGURATION
PGND
IN
C
BST1
0603
EN
POKB/INTB
V
IO
SCL
SDA
NOTE: PLACE C AND C
IN OUT
Figure 15. Layout Recommendation for 16 FC2QFN Package with 4mm x 4mm Inductor
www.analog.com
) and output capacitors (C
IN
LX1
L
4.0mm x 4.0mm
BST1
+
V
L
AGND
CLOSE TO THE IC TO MINIMIZE PA RASITIC INDUCTANCE WI THIN THE LOOP
) immediately next to the IN pin and OUT pin of the IC,
OUT
) as short as possible. Prioritize C
BST
LX2
BST2
C
BST2
0603
FB
*USING INTERNAL
SEL
FEEDB ACK RESISTORS
MAX77857Q Evaluation Kit
Tutorial 5527 for more information.
LEGEND
4.0mm x 4.0mm
PGND
OUT
VIA 8mil HOLE, 16mil PAD
COMPONE NT SIZES LI STED IN IMPE RIAL
UNLES S OTHERWISE SPE CIFIED
placement to
BST
0805
0603
0402
Analog Devices | 13