One problem with writing an Application Note on PCB layout is that the people who read it are usually not the ones who are going to use it. Even if the designer has struggled through electromagnetic fields, EMC, EMI, board parasitics, transmission line effects, grounding, etc., he will in all probability then go on with his primary design task, leaving the layout to the CAD/layout person. Unfortunately, especially when it comes to switching regulators, it is not enough to be concerned with just basic routing/connectivity and mechanical issues.
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National Application Note download PDF