App note: Board layout tips for switchmode DC/DC converters

The app note featured here provides basic PCB layout tips for building switch-mode DC/DC converters. As an integral part of their function, switch mode converters have square like signals in some of their traces. These signals create harmonics from the switching frequency that can cause much EMI interference, as well as decreased stability of the converter.

This note by Maxim helps eliminate these and some other issues that might arise form using switch-mode converters.

  1. Place and route the power components. Start placing switching transistors Q1
    and Q2, inductor L, and input and output capacitors CIN and
    COUT. Arrange them so as to minimize the distances between them, in
    particular the ground connections of Q2, CIN and COUT, and
    the CIN and Q1 connection. Next, create top-layer shapes for the
    power ground, input, output, and LX nodes, and route them on the top layer using
    wide short traces.
  2. Place and route the low-level signal components. The controller IC should be
    placed close to the switching transistors. Low-level signal components are
    placed on the other side of the controller. High-impedance nodes are kept small
    and away from the LX node. Create an analog ground shape on a suitable layer and
    connect it to power ground at one point.

Instructions from this article can be used whenever one needs to route high current square like signals, like PWM power signals.

Image by C J Cowie: CC BY-SA

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1 Comment

  1. I’m thinking about how they would eliminate the square waves by using sine waves with a constant difference but it seems it would only move the square waves to another part of the circuit and then add low-frequency RF noise to the output. It seems that after all the extra filters that would have be added, this would be a wasted effort? Doubling or tripling the amount of filters would not make sense.

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