Introduction

A great many customer "complaints" regarding switcher ICs are ultimately traced to poor PCB (printed circuit board) layout practices. When designing a PCB for a switching regulator, we need to be aware that the final product is going to be only as good as its layout. Certainly, some ICs are more noise sensitive than others. Sometimes, the "same" part from several vendors can also have starkly varying noise sensitivities (see Appendix 1 for a case involving the popular 384x series). Further, some ICs are architecturally more noise sensitive than others (for example current mode controllers are far more "layout-sensitive" than voltage mode controllers). We also have to face the fact that virtually no semiconductor manufacturers characterize the noise sensitivity of their products (often letting the customers discover it for themselves!). However, as designers, we can certainly, with poor attention to layout, pull off the near-impossible turn a comparatively stable IC into a jittery and nervous part one that can malfunction and even cause catastrophic consequences (switch failure). Further, since very few of these problems can be easily corrected, or "band-aided," at a later stage, it is very important to get the layout right at the very beginning.

Most of the layout recommendations in this chapter revolve around simply assuring basic functionality and performance. Though luckily, the beleaguered switcher designer will be happy to know, in general, the electrical aspects are all related pointing in the same general direction. So for example, a good layout, that is,...