LM3204

SNVS351C – JUNE 2005 – REVISED APRIL 2013

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between these components carry relatively high switching currents and act as antennas. Following this rule

reduces radiated noise. Place the capacitors and inductor close to the LM3204. The input capacitor should

3. Arrange the components so that the switching current loops curl in the same direction. During the first half of

each cycle, current flows from the input filter capacitor, through the LM3204 and inductor to the output filter

capacitor and back through ground, forming a current loop. In the second half of each cycle, current is pulled

up from ground, through the LM3204 by the inductor, to the output filter capacitor and then back through

ground, forming a second current loop. Routing these loops so the current curls in the same direction,

prevents magnetic field reversal between the two half-cycles and reduces radiated noise.

4. Connect the ground pins of the LM3204, and filter capacitors together using generous component side

copper fill as a pseudo-ground plane. Then connect this to the ground-plane (if one is used) with several

vias. This reduces ground plane noise by preventing the switching currents from circulating through the

ground plane. It also reduces ground bounce at the LM3204 by giving it a low impedance ground connection.

5. Use wide traces between the power components and for power connections to the DC-DC converter circuit.

This reduces voltage errors caused by resistive losses across the traces.

6. Route noise sensitive traces, such as the voltage feedback trace, away from noisy traces and components.

The voltage feedback trace must remain close to the LM3204 circuit and should be routed directly from FB

have a ground plane between the top layer and the layer on which the feedback trace is routed. This reduces

EMI radiation on to the DC-DC converter’s own voltage feedback trace.

connecting it directly to the FB pin for better noise immunity.

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