AN2837 Datasheet, PDF (8/12 Pages) STMicroelectronics – Positive to negative buck-boost converter

PCB layout guidelines
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PCB layout guidelines
AN2837
A recommended printed circuit board (PCB) layout for the ST1S03 inverting regulator is
shown in Figure 9. It is very important to place the input capacitor as close as possible to the
input pin of the regulator. In order to achieve the best performance, special care must be
taken to ensure proper grounding. A good practice is to always use a separate ground
plane, or at a minimum a single point ground structure.
High switching currents may cause voltage drops in the PCB metal trace, and long metal
traces and component leads cause unwanted parasitic inductance as well, especially at
switching frequencies of 1.5 MHz. This parasitic inductance is very often the main source of
EMI problems and high voltage spikes at input and output lines. Therefore, place the
inductor, freewheeling diode, and especially the input capacitor as close as possible to the
device. Use big lines for the metal traces to these components. Wire the feedback circuit
away from the inductor to avoid flux intersection. The use of a ground ring guard is
recommended. Use shielded cores for better EMI performance. Capacitors with low ESR
are recommended the for inputs and outputs.
Figure 9. PCB layout - top side
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