DC/DC converter PCB layout, Part 1

June 23, 2015 //By Timothy Hegarty
DC/DC converter PCB layout, Part 1
Timothy Hegarty of Texas Instruments considers how PCB layout design can play a critical role in solving a power converter puzzle.

Fundamental to careful system design of any DC/DC power converter is a well-planned and carefully executed printed circuit board (PCB) layout. An optimized layout leads to better performance, lower cost and faster time-to-market. Additionally, it can constitute a competitive advantage for the end equipment user owing to higher reliability (lower component temperature), easier regulatory compliance (lower conducted and radiated emissions), and improved space utilization (reduced solution volume and footprint).

A primary objective of this three-part article series is to look closely at PCB layout design, knowing that it represents a critical piece of the power converter puzzle. These articles also offer clear guidance on factors related specifically to PCB design to achieve low noise converter implementations. Using a four-switch synchronous buck-boost DC/DC converter as a case study, PCB layout considerations for fast-switching, high-current applications are highlighted using a step-by-step process. The real purpose here is a practical one. PCB layout, one of the thorniest and most menacing topics for a power supply engineer, can make or break a real design.

Four-switch buck-boost converter review
 
Let’s digress for a moment to introduce the four-switch (non-inverting) synchronous buck-boost topology. This circuit is an excellent example to study DC/DC converter PCB layout. It has  numerous applications including industrial computing, LED lighting, RF power amplification, and USB power delivery [1] . The most compelling feature of this particular buck-boost implementation is that buck, boost, and buck-boost transition modes are engaged as needed to achieve high efficiency across wide and overlapping input and output voltage ranges.

One common application scenario is deriving a tightly-regulated 12V rail from an automotive battery source. Even if the battery’s DC voltage varies from 9V to 16V, transients arise from start/stop, cold crank or load dump. [2]
The voltage during such events can dip as low as 3V or spike to 42V, sometimes even higher. To meet these requirements, the schematic in Figure 1 illustrates components for the power

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