Rainbow Electronics MAX17075 - Manual (Page 21)

PCB Layout and Grounding
Careful PCB layout is important for proper operation.
Use the following guidelines for good PCB layout:
• Minimize the area of high-current loops by placing
the inductor, the output diode, and the output
capacitors near the input capacitors and near the
LX and PGND pins. The high-current input loop
goes from the positive terminal of the input capaci-
tor to the inductor, to the IC’s LX pin, out of PGND,
and to the input capacitor’s negative terminal. The
high-current output loop is from the positive terminal
of the input capacitor to the inductor, to the output
diode (D1), and to the positive terminal of the output
capacitors, reconnecting between the output
capacitor and input capacitor ground terminals.
Connect these loop components with short, wide
connections.
• Avoid using vias in the high-current paths. If vias
are unavoidable, use many vias in parallel to
reduce resistance and inductance.
• Create a power-ground island (PGND) consisting of
the input and output capacitor grounds, PGND pin,
and any charge-pump components. Connect all
these together with short, wide traces or a small
ground plane. Maximizing the width of the power
ground traces improves efficiency and reduces out-
put voltage ripple and noise spikes. Create an ana-
log ground plane (AGND) consisting of the AGND
pin, all the feedback-divider ground connections,
the operational amplifier divider ground connec-
tions, the COMP and DEL capacitor ground con-
nections, and the device’s exposed backside
paddle. Connect the AGND and PGND islands by
connecting the PGND pin directly to the exposed
backside paddle. Make no other connections
between these separate ground planes.
• Place all feedback voltage-divider resistors within
5mm of their respective feedback pins. The
divider’s center trace should be kept short. Placing
the resistors far away causes their FB traces to
become antennas that can pick up switching noise.
Take care to avoid running any feedback trace near
LX or the switching nodes in the charge pumps, or
provide a ground shield.
• Place the VCC pin and REF pin bypass capacitors
as close as possible to the device. The ground con-
nection of the VCC bypass capacitor should be
connected directly to the AGND pin with a wide
trace.
• Minimize the length and maximize the width of the
traces between the output capacitors and the load
for best transient responses.
• Minimize the size of the LX node while keeping it
wide and short. Keep the LX node away from feed-
back nodes (FB, FBP, and FBN) and analog
ground. Use DC traces to shield if necessary.
Refer to the MAX17075 evaluation kit for an example of
proper PCB layout.
MAX17075
Boost Regulator with Integrated Charge Pumps,
Switch Control, and High-Current Op Amp
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