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Board Layout Considerations

components. This reduces EMI radiated onto the DC-DC converter’s own voltage feedback trace.

7. Place noise sensitive circuitry, such as radio IF blocks, away from the DC-DC converter, CMOS digital

blocks and other noisy circuitry. Interference with noise-sensitive circuitry in the system can be reduced

through distance.

In mobile phones, for example, a common practice is to place the DC-DC converter on one corner of the

board, arrange the CMOS digital circuitry around it (since this also generates noise), and then place

sensitive preamplifiers and IF stages on the diagonally opposing corner. Often, the sensitive circuitry is

shielded with a metal pan and power to it is post-regulated to reduce conducted noise, using low-dropout

linear regulators.

SNVA312B–May 2008–Revised April 2013 AN-1772 LM3691 Evaluation Board

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