Power Supply Circuits on PCBs: Place the Critical Loop Before General Routing

A power supply circuit on a PCB may regulate an existing DC source, convert between DC levels or form part of an AC-powered system. This layout guide focuses on the review method for a selected converter, not a universal circuit or a procedure for working on live mains equipment.

Start from the exact device and package

Use the controller or regulator data sheet, its recommended components and its layout section. Package pinout matters: two versions of a device can need different placement. Check the reference design’s assumptions before transferring its geometry to a different board.

For example, TI’s LMR33630-Q1 guidance discusses the input capacitor loop and feedback-divider placement. Those are device-specific directions that illustrate the review method; they should not be copied blindly to an unrelated topology.

Draw the current paths before placing parts

Identify which paths carry rapidly changing current and which carry the measured feedback information. Place the relevant capacitors, switching devices and return connections so their geometry supports the data-sheet guidance. Review the loop area, not only the distance between component bodies.

• Check the input source and local bypass connection.
• Identify the switching node and its nearby sensitive routes.
• Review the output and load-return path.
• Keep sensing connections tied to the intended measurement points.
• Inspect every via or narrow copper transition in the power path.

Do not complete ordinary signal routing first and squeeze the power stage into the remaining space. Its placement often determines whether later routing can be kept sensible.

Review heat and mechanics

Use the actual package thermal recommendations and intended enclosure conditions. Provide the necessary copper and attachment arrangement without creating accidental electrical connections to mounting hardware. Check component height and access to terminals under the real assembly constraints.

Coordinate large copper areas and thermal pads with the assembler. A layout change that improves heat distribution can affect soldering and should be reviewed as part of the populated board.

Test the requirement, not just the output voltage

Plan measurements for the operating conditions relevant to the product, including load changes or startup where required. Record instrument connections and probe arrangements so noise measurements remain interpretable. Compare the measured board with the actual released construction and component set. Record any temporary wires or probe modifications because they can change the behavior being measured.

Primary reference: TI LMR33630-Q1 data sheet and layout guidance. Use the DFM checklist and test planning guide to complete the release and verification record.