Electrostatic Protection in PCB Design
In practical circuit design, we will adopt one or several of the following methods to carry out electrostatic protection:
1. Avalanche Diode for Electrostatic Protection
This is also a method often used in design. Typical method is to connect an avalanche diode to the ground in parallel with the key signal line. This method uses avalanche diodes to respond quickly and have the ability to clamp stably. It can consume aggregated high voltage in a short time to protect circuit boards.
2. Using High Voltage Capacitor for Circuit Protection
This method usually places the ceramic capacitor withstanding at least 1.5KV at the position of I/O connector or key signal, and the connection line is as short as possible to reduce the inductance of the connection line. If the capacitor with low voltage withstanding is used, it will cause the damage of capacitor and lose the protection function.
3. Circuit protection with ferrite beads
Ferrite beads can attenuate ESD current and suppress radiation. When faced with two problems, a ferrite bead would be a good choice.
4. Spark gap method
This method can be seen in one material. The microstrip line layer consisting of copper sheet is composed of triangular copper sheet with pointed points aligned with each other. One end of the triangular copper sheet is connected to the signal line, and the other is connected to the ground of the triangular copper sheet. When there is static electricity, it will produce tip discharge and consume electric energy.
5. Using LC filter to protect circuit
The filter composed of LC can effectively reduce the high frequency electrostatic entry into the circuit. The inductance characteristic of inductor can well restrain the high frequency ESD from entering the circuit, while the capacitor shunts 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 with less RF effect, and its performance has been further improved in signal integrity.
6. ESD Protection of Multilayer Board
When funds permit, choosing multi-layer board is also an effective way to prevent ESD. In a multilayer board, with a complete ground plane close to the line, ESD can be more quickly coupled to the low impedance plane, thereby protecting the role of key signals.
7. Protection Method of Circuit Board Peripheral Protection Belt
This method usually draws the route without welding layer around the circuit board. When conditions permit, the line is connected to the housing. At the same time, it should be noted that the line can not form a closed loop, so as not to cause more trouble by forming a ring antenna.
8. Circuit protection using CMOS devices or TTL devices with clamping diodes
This method uses the principle of isolation to protect circuit boards. Because these devices are protected by clamping diodes, the design complexity is reduced in practical circuit design.
9. Use decoupling capacitors more often
These decoupling capacitors should have low ESL and ESR values. For low frequency ESD, the decoupling capacitors reduce the area of the loop. Because of the role of ESL, the electrolyte action is weakened and the high frequency energy can be filtered better.
In a word, although ESD is terrible, it may even bring serious consequences, but only by protecting the power supply and signal lines in the circuit, can ESD's current flow into PCB be effectively prevented. Among them, my boss often said that "a good grounding of a board is the king's way", I hope this sentence can also bring you the effect of breaking the skylight.
