Case Study on ESD Design Rectification for In-Vehicle Entertainment Systems

Case Study on ESD Design Rectification for In-Vehicle Entertainment Systems

1. Product Description

Some entertainment audio-visual vehicle machine, power interface DC24V input, multi-button operation control, multiple external IO output control interfaces,
LCD screen display.The appearance of the operation panel is a full plastic shell, and the motherboard and LCD screen are fixed with metal screws.Static electricity test requirements contact discharge 8KV and air discharge 15KV.

2. ESD Test Results and Problem Description

a) Contact discharge on the fixed metal screws of the motherboard causes the operation panel to freeze, and the control indicator light flashes.

b) Air discharge on the LCD display panel, without releasing an arc, can cause the operation panel to freeze and restart.

3. Product Problem Analysis

Product problem analysis (may involve structural changes, single board, schematic, power supply)
Through analysis, the product has the following problems:
1) The metal screws fixing the motherboard exposed in the casing have no connection to the ground. When contact discharge occurs on the metal screws, the arc discharges to the motherboard, causing it to freeze.
2) The wiring of buttons and I/O ports is long and lacks protective filtering, making it easy for static interference to couple directly to the motherboard, causing system freeze.

Case Study on ESD Design Rectification for In-Vehicle Entertainment Systems

Case Study on ESD Design Rectification for In-Vehicle Entertainment Systems

3) The power pins of the CPU lack capacitive filtering, making it susceptible to static interference, causing freezes.

Case Study on ESD Design Rectification for In-Vehicle Entertainment Systems

4) The RST signal routing is sensitive and lacks filtering protection, making it easy to cause system freeze and reset.Need to add protective filtering.
5) The PCB is a two-layer board, and many signal routes lack ground reference, leading to large signal loops that easily couple static interference.

Case Study on ESD Design Rectification for In-Vehicle Entertainment Systems

6) The PCB is close to the edge of the board, making it susceptible to static interference.

Case Study on ESD Design Rectification for In-Vehicle Entertainment Systems

4. Product Rectification Plan and Test Data

1) Connect the digital ground of the PCB to the screw hole with a 102 capacitor, which provides isolation from static interference and a discharge path.
2) For I/O ports, display ports, and button display ports, use LC filtering, where L is an inductor and C is a 33pF capacitor.
3) Add multiple 102 capacitors to the CPU power supply to ensure that at least one capacitor filters 1-3 pins.
4) Add a 5V TVS diode near the reset signal to form an LC circuit.
5) Change the PCB to a four-layer structure, with specific layers as S1-G-P-S2.G is a complete ground layer, divided into digital ground and analog ground, connected with multiple 0-ohm resistors.P is mainly for power, primarily a 3.3V supply.S1 and S2 are the two main routing layers.Sensitive signals need to be ground-coupled and grounded.
For the revised prototype, final validation showed contact discharge reached 9KV and air discharge reached 11KV, passing the test.

5. Case Summary

(1) Static interference is mainly common-mode interference, and the shortest path for static interference should be released to ground.Contact discharge directly releases interference to the product, mainly using discharge protection.Discharge is to release static interference to the ground through the nearest path.Prevent interference from subsequent stages.Protective devices mainly include TVS diodes, capacitors, inductors, etc.

(2) For air discharge, the main interference comes from indirect discharge and spatial field interference.Measures against indirect discharge include isolation and discharge protection.Isolation increases the distance and insulation of discharge points so that the product has no release points.Spatial field interference is a serious static interference.Subsequent rectification is also challenging.It mainly relates to the overall PCB design, including PCB layer distribution, power, and ground design.

(3) The static issues of this project mainly involve the discharge of static electricity from the shell, large circuit board loops, and long wiring, which easily couple static interference.

Case Study on ESD Design Rectification for In-Vehicle Entertainment Systems

Case Study on ESD Design Rectification for In-Vehicle Entertainment Systems

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Case Study on ESD Design Rectification for In-Vehicle Entertainment Systems

Case Study on ESD Design Rectification for In-Vehicle Entertainment Systems

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