Grounding Considerations in DC/DC PCB Layout
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Grounding Considerations in DC/DC PCB Layout

Posted Date: 2024-01-19

This article will discuss the "grounding" related content in the PCB layout of the boost DC/DC converter. We often hear statements such as “grounding is important” and “grounding design needs to be strengthened”. In fact, in the PCB layout of the boost DC/DC converter, insufficient consideration of grounding and grounding design that deviates from basic rules are the root cause of problems. Please recognize that the following precautions need to be strictly adhered to. Additionally, observing these precautions is not limited to step-up DC/DC converters.

ground

First, the analog small signal ground and power ground must be separated. In principle, the layout of the power ground does not need to be separated from the top layer with lower wiring resistance and good heat dissipation.

If the power ground is separated and connected via vias on the back, losses and noise will be worsened by the via resistors and inductors. The practice of setting a ground layer on the inner layer or back for the purpose of shielding, heat dissipation and reducing DC losses is only auxiliary grounding.

The circuit board layout for this example. This is a basic layout example of the power ground (PGND, orange section) and analog small signal ground (AGND, light blue section) on the top layer.

When designing the ground layer on the inner layer or back of a multi-layer circuit board, special attention needs to be paid to the grounding of power supplies with high frequency switching noise. If the second layer has a power ground plane designed to reduce DC losses, use multiple vias to connect the top layer to the second layer to reduce the impedance of the power ground.

Also, if you have a common ground on the third layer and a signal ground on the fourth layer, then the connection between the power ground and the third and fourth layer grounds only connects the power supply near the input capacitor where high frequency switching noise is less Ground. Never connect noisy outputs or freewheeling diodes to power ground. See schematic cross-section below.

Key takeaways:

In the PCB layout of the boost DC/DC converter, AGND and PGND need to be separated.

In principle, the PGND in the PCB layout of the boost DC/DC converter is configured on the top layer without separation.

In the PCB layout of a step-up DC/DC converter, if PGND is separated and connected via a via on the back side, loss and noise will increase due to the influence of via resistance and inductance.

In the PCB layout of the boost DC/DC converter, when configuring the ground layer on the inner layer or back of the multi-layer circuit board, attention needs to be paid to the connection between the input terminal and the diode PGND, which has more high-frequency switching noise.

In the PCB layout of the boost DC/DC converter, the connection between the top layer PGND and the inner layer PGND must be connected through multiple vias to reduce impedance and reduce DC losses.

In the PCB layout of the boost DC/DC converter, the connection between the common ground or signal ground and PGND should be done at the PGND near the output capacitor with less high-frequency switching noise, and not near the input terminal or diode with more noise. PGN connection.


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