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 feedback network, resistor
RFBT and RFBB, should be kept close to the FB pin.
VOUT sense path away from noisy nodes and preferably through a
layer on the other side of a shielding layer.
- The input bypass capacitor
CIN must be placed as close as possible to the VIN pin and
ground. Grounding for both the input and output capacitors should consist of
localized top side planes that connect to the GND pin and PAD.
- The inductor L should be placed
close to the SW pin to reduce magnetic and electrostatic noise.
- The output capacitor,
COUT should be placed close to the junction of L and the diode D.
The L, D, and COUT trace should be as short as possible to reduce
conducted and radiated noise and increase overall efficiency.
- The ground connection for the
diode, CIN, and COUT should be as small as possible and
tied to the system ground plane in only one spot (preferably at the
COUT ground point) to minimize conducted noise in the system
ground plane.
- For more detail on switching
power supply layout considerations see SNVA021 Application Note
AN-1149.