11.1 Layout Guidelines
Layout is a critical portion of good power supply design. The following guidelines will help users design a PCB with the best power conversion performance, thermal performance, and minimized generation of unwanted EMI.
- The input bypass capacitor CIN must be placed as close as possible to the VIN and GND pins. Grounding for both the input and output capacitors should 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 should 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 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. Ensure enough copper area is used for heat-sinking to keep the junction temperature below 125 °C.