Layout is a critical portion of good power supply
design. The following guidelines help users design a PCB with the best power
conversion performance, thermal performance, and minimized generation of unwanted
EMI.
- Place the input bypass capacitor CIN
as close as possible to the VIN and GND pins. Grounding for both the input and
output capacitors must consist of localized top side planes that connect to the
GND pin.
- Minimize trace length to the FB pin net. Both feedback resistors, RFBT and RFBB, must be located close to the FB pin. If VOUT accuracy at the load is important, make sure VOUT sense is made at the load. Route VOUT sense path away from noisy nodes and preferably through a layer on the other side of a shielded layer.
- Use ground plane in one of the middle layers as noise shielding and heat dissipation path if possible.
- Make VIN, VOUT, and ground
bus connections as wide as possible. This action reduces any voltage drops on
the input or output paths of the converter and maximizes efficiency.
- Provide adequate device heat-sinking. GND, VIN,
and SW pins provide the main heat dissipation path, make the GND, VIN, and SW
plane area as large as possible. Use an array of heat-sinking vias to connect
the top side ground plane to the ground plane on the bottom PCB layer. If the
PCB has multiple copper layers, these thermal vias can also be connected to
inner layer heat-spreading ground planes. Make sure enough copper area is used
for heat-sinking to keep the junction temperature below 150°C.