Grounding-PCB layout of step-up DC/DC converter

“This article will discuss the “grounding” related content in the PCB layout of the step-up DC/DC converter. It is often heard that “grounding is very important”, “the grounding design needs to be strengthened” and so on. In fact, in the PCB layout of the step-up DC/DC converter, the grounding design that does not fully consider the grounding and deviates from the basic rules is the source of the problem. Please realize that the following precautions need to be strictly observed. In addition, compliance with these precautions is not limited to step-up DC/DC converters.

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This article will discuss the “grounding” related content in the PCB layout of the step-up DC/DC converter. It is often heard that “grounding is very important”, “the grounding design needs to be strengthened” and so on. In fact, in the PCB layout of the step-up DC/DC converter, the grounding design that does not fully consider the grounding and deviates from the basic rules is the source of the problem. Please realize that the following precautions need to be strictly observed. In addition, compliance with these precautions is not limited to step-up DC/DC converters.

Grounded

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 low wiring resistance and good heat dissipation.

If the power ground is separated and connected to the back side via vias, the loss and noise will deteriorate due to the influence of via resistance and inductors. The practice of setting a grounding layer on the inner layer or the back for shielding, heat dissipation and reducing DC loss is only an auxiliary grounding.

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

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

In addition, if there is a common ground on the third layer and a signal ground on the fourth layer, the connection between the power ground and the third and fourth layer grounds is only connected to the power supply near the input capacitor with low high-frequency switching noise Grounded. Do not connect the noisy output or the power supply ground of the freewheeling diode. See the schematic cross section below.

Key points:

・ In the PCB layout of the step-up DC/DC converter, AGND and PGND need to be separated.
・ In principle, the PGND in the PCB layout of the step-up DC/DC converter is placed on the top layer without separation.
・ In the PCB layout of the step-up DC/DC converter, if PGND is separated and connected on the back side via via holes, the loss and noise will increase due to the influence of via hole resistance and inductance.
・ In the PCB layout of the step-up DC/DC converter, when the ground layer is arranged on the inner layer or the back of the multilayer circuit board, it is necessary to pay attention to the connection between the input terminal and the diode PGND with high frequency switching noise.
・ In the PCB layout of the step-up DC/DC converter, the connection between the top layer PGND and the inner layer PGND should be connected through multiple vias to reduce impedance and reduce DC loss.
・ In the PCB layout of the step-up DC/DC converter, the connection between the common ground or signal ground and PGND should be made at the PGND near the output capacitor with less high-frequency switching noise, and not at the noisy input terminal or diode PGN connection nearby.