Grounding wire layout techniques in DC/DC converter design

When designing a printed circuit board, design engineers will carefully consider the copper wire routing and component placement. If these two points are not fully considered, the efficiency, maximum output current, output ripple and other characteristics of the printed circuit board will be affected. The two main reasons for these effects are the connection of the ground wire (GND, VSS) and the power line (+B, VCC, VDD). If the ground wire and power line are designed reasonably, the circuit will work normally and obtain better performance indicators. Otherwise, interference and performance deterioration will occur. This article introduces some general design principles and ground connection methods for the design of DC/DC converters.

1. Design principles

The layout of printed lines and the placement of components often affect the performance of the circuit. The following are four principles for grounding line design:

1. Use planar pattern for grounding;

2. Connect the power cord using a flat wiring method;

3. Place components one by one according to the signal current direction in the circuit diagram;

4. The data obtained from the experiment should not be adjusted in any way when applied, and should be reproduced as is even if it is affected by the size of the plate or other factors.

Paying attention to the above principles and key points in design can reduce circuit noise and signal interference. In addition to the above basic principles, the following two points should be kept in mind when designing copper wire routing patterns and component placement: stray capacitance will be generated between wiring; the length of the connection will generate impedance. Paying attention to stray capacitance between wires and shortening the wiring length in the design will help eliminate noise and reduce radiation.

Based on the above basic principles, design engineers should pay attention to the following points (see Figure 1):

1. Layout components according to the circuit schematic, and distinguish between input current lines and output current lines;

2. Place components appropriately to ensure that the wires between them are as short as possible to reduce noise;

3. Careful design should be taken to reduce noise in areas where voltage changes greatly and where high current flows;

4. If coils and transformers are used in the circuit, the connections must be made carefully;

5. When designing the circuit, place the components in the same direction to facilitate reflow soldering;

6. A gap of more than 0.5 mm must be maintained between components or between component pads to avoid bridging.

2. PCB Design Example

a. Boost Converter Mode Wiring

In a boost converter, the location of the output capacitor (CL) is more important than any other component, see Figure 2.

It is recommended to pay attention to the following two points when designing PCB:

1. Place the output capacitor as close to the IC as possible to minimize the current loop.

2. Use a planar wiring method to connect the ground wire on the back of the PCB board. The ground wire on the back of the board should be connected to the ground wire on the front of the board through a via.

b. Buck converter wiring

In the buck circuit design, the location of the Schottky diode is critical, as shown in Figure 3.

Pay attention to the following points in PCB design:

1. The design of the Schottky diode grounding point will affect the output stability;

2. The length of the Schottky diode cathode connection line will affect the output stability;

3. A large area of ​​copper foil is used as the ground on the back of the PCB, which is connected to the front ground through vias.