Engineer skills: illustrating how to use shielding and absorbing materials to solve electromagnetic compatibility (EMC) radiation problems

1.1. Analysis of PCB layout design issues

1.1.1. Analysis of Problem 1

[Problem Analysis] Improper placement of the filter component at the input end of the DC12V power interface can lead to the failure of the filtering performance of the filter component;

The CAN interface input filter component is placed too far away, resulting in poor filtering effect;

Suggestions for Improving Problems

(1) Filter devices such as capacitors and differential mode inductors should be placed near the interface and arranged according to the current flow direction;

(2) The negative electrode is wired side by side with the positive electrode in the form of a wire, passing through a differential mode inductor near the interface and leading to the power chip;

(3) The interface and its projection area require excavation to avoid the failure of the negative differential inductance filter;

(4) The filtering common mode inductor of the CAN interface is placed near the interface;

The specific layout is shown in the following figure:

1.1.2. Analysis of Problem 2

[Problem Analysis] Improper placement of input and output filtering components in the power chip can result in poor filtering performance;

Suggestions for improving the problem: The input and output wiring of the power chip should be separated as much as possible, and the filtering devices should be placed neatly and compactly near the chip end according to the signal flow direction;

The specific layout of the power chip can refer to the following figure:

1.2. Analysis of PCB Grounding Design Issues

1.2.1. Analysis of Problem 1

[Problem Analysis] Improper division of the power layer can lead to significant cross division issues between adjacent wiring layers due to excessive power division; Suggestions for Improving Problems

(1) Fully lay 3.3V and DDR power supplies in the power layer to ensure the integrity of the power layer as much as possible;

(2) AVDD/DVDD/5V can be processed in the 3rd and 4th wiring layers, and it is recommended not to divide them in the power layer (second layer) as much as possible;

1.2.2. Analysis of Problem 2

Problem analysis: When laying a large area of ground on the top or bottom floor, there are only a few through holes, which leads to incomplete ground plane connections and is not conducive to electromagnetic compatibility;

Suggestions for improving the problem: When laying a large area of ground on the surface or bottom, it is required to drill more ground holes to connect with the lower ground level, in order to avoid the phenomenon of "islands";

1.3. Analysis of PCB wiring design issues

1.3.1. Analysis of Problem 1

[Problem Analysis] Improper routing of CAN signals can easily couple with external interference, leading to EMC and other issues;

Suggestions for Improving Problems

(1) The CAN signal wiring from the interface to the CAN chip should strictly follow the differential wiring rules;

(2) The CAN signal routing from the CAN chip to the CPU requires that each signal line be grounded, and the grounding wire should be connected to the lower ground plane through multiple ground holes;

(3) Do not pass the wiring through the cable interface;

1.3.2. Analysis of Problem 2

[Problem Analysis] Improper wiring handling from DSP chip to cable interface;