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PCB Layout Considerations

9 PCB Layout Considerations

The evaluation board layers from top to bottom are:

1. Top, component side

2. Ground plane

3. Mid signal section

4. Bottom, solder side

For good performance of the circuit, it is essential to place the input and output capacitors very close to

the circuit and use wide routing for the traces allowing high currents.

Sensitive components should be placed far from those components with high pulsating current.

Decoupling capacitors should be close to circuit’s V

pins. Digital and analog ground should be routed

separately and connected together in a star connection.

It’s good practice to minimize high current and switching current paths.

9.1 Low Drop Out Regulators

Place the filter capacitors very close to the input and output pins. Use large trace width for high current

carrying traces and the returns to ground.

9.2 Buck Regulators

Place the supply bypass, filter capacitor, and inductor close together and keep the traces short. The traces

between these components carry relatively high switching current and act as antennas. Following these

rules reduces radiated noise.

Arrange the components so that the switching current loops curl in the same direction.

Connect the buck ground and the ground of the capacitors together using generous component-side

copper fill as a pseudo-ground plane. Then connect this back to the general board system ground plane at

a single point. Place the pseudo-ground plane below these components and then have it tied to system

ground of the output capacitor outside of the current loops. This prevents the switched current from

injecting noise into the system ground. These components along with the inductor and output should be

placed on the same side of the circuit board, and their connections should be made on the same layer.

SNVA329D–March 2008–Revised April 2013 AN-1800 Evaluation Kit for LM26480 - Dual DC/DC Buck Regulators with

Dual Low-Noise Linear Regulators

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