Electrostatic protection that engineers must know
In the actual circuit design, we will use one or more of the following methods for electrostatic protection:
1. Avalanche diode for electrostatic protection
This is also a method often used in design. Typically, an avalanche diode is connected to the ground at a critical signal line.
The method is based on the fast response of avalanche diode and the ability of stable clamp, which can consume the concentrated high voltage and protect the circuit board in a short time.
2. High voltage capacitor is used for circuit protection
In this practice, ceramic capacitors with a withstand voltage of at least 1.5kv are usually placed at the I/O connector or critical signal position, and the connection wire should be as short as possible to reduce the inductive resistance of the connection wire. If a low voltage capacitor is used, the capacitor will be damaged and lose its protective effect.
3. Iron and oxygen magnetic beads are used for circuit protection
Iron oxide magnetic beads can well attenuate ESD current and inhibit radiation. When faced with two problems, an iron bead is a good choice.
4. Spark gap method
This method is seen in one of the materials, where the microstrip wire layers of copper are formed using triangular copper plates with the tips pointed at each other, one end of which is connected to the signal wire and the other to the ground. When there is static electricity, it produces a tip discharge that consumes electricity.
5. LC filter is adopted to protect the circuit
The filter composed of LC can effectively reduce the high-frequency static electricity into the circuit. The inductive reactance of the inductor can well inhibit the high-frequency ESD entering the circuit, while the capacitor shunt the high-frequency energy of ESD to the ground. At the same time, this type of filter can also smooth the edge of the signal and reduce the RF effect, the performance of the signal integrity has been further improved.
6. Multi-layer board for ESD protection
When funds allow, the choice of multi-layer board is also an effective means to prevent ESD. In a multilayer plate, with a complete ground plane close to the wiring, ESD can be more quickly coupled to the low impedance plane, thus protecting the role of key signals.
7. Circuit board peripheral protection belt method protection
This method is usually in the circuit board around the drawing without welding layer line. When conditions permit, connect the cable to the shell, and pay attention that the cable cannot form a closed loop, so as to avoid more trouble caused by the formation of a ring antenna.
8. CMOS or TTL devices with clamping diodes are used for circuit protection
This method makes use of the isolation principle to protect the circuit board, because these devices have the protection of clamping diode, reducing the complexity of the design in the actual circuit design.
9. More decoupling capacitors are adopted
These decoupling capacitors should have low ESL and ESR values. For low-frequency ESD, the decoupling capacitors reduce the area of the loop, and the effect of ESL weakens the effect of electrolyte, so that the high-frequency energy can be better filtered.
In a word, although ESD is terrible and may even bring serious consequences, only by protecting the power supply and signal line on the circuit, can ESD's current flow into the PCB be effectively prevented.