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ESD device protection principle and selection is how, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain in detail for you, people with this need can come to learn, I hope you can gain something.

1. Normally, the ESD protection circuit is as follows

2. When the system has no interference and works normally, the ESD device can be ignored and almost has no effect.

3. When the external interface voltage exceeds the breakdown voltage (VBR) of the ESD device, the ESD device begins to function and diverts the current to the ground.

4. The difference between the working voltage (VRWM) of the actual ESD device and the breakdown voltage (VBR). When selecting the ESD device, the operating voltage of the system is lower than that of the ESD device (VRWM).

For example, if the system is 05V, then we should choose a TVS with an operating voltage (VRWM) greater than 5V.

5. Unidirectional ESD devices and bi-directional ESD devices, bi-directional ESD devices can pass through the signal of positive and negative breakdown voltage (VBR), while unidirectional ESD devices can only pass the signal of positive breakdown voltage (VBR). If it passes through negative, it will cause breakdown of ESD devices.

6. The characteristics of bi-directional ESD devices and unidirectional ESD devices, unidirectional ESD devices provide better protection for negative voltage.

7. Several ESD models and their discharge curves.

8. IEC 61000-4-2 is the daily contact level, which is divided into four levels.

9. However, when the ESD device conforms to IEC 61000-4-2, it only represents the protection of the ESD device itself, and does not mean that the later circuit can withstand the corresponding impact. Clamp voltage is a measure of the ability of the ESD device to protect the circuit system. The clamp voltage is the shock when the external circuit passes through the ESD device. As shown in the picture, the red is the shock, and the blue is the clamp voltage after the impact of the ESD device. We can choose the clamp voltage according to our own system requirements.

10. In practical application, ESD devices have parasitic capacitance, such as the influence of parasitic capacitance on high-speed circuit interface, parasitic capacitance will affect the speed of level rise and fall, such as USB3.0, HDMI and so on.

11. When selecting ESD devices, the parasitic capacitance can be selected according to the application interface, as shown in the following figure

Selection steps of ESD device

1. Calculate the range of interface signal amplitude to determine the operating voltage of ESD devices.

two。 Use unidirectional or bidirectional ESD devices according to the type of signal

3. The maximum parasitic capacitance of the interface is determined according to the signal rate.

4. According to the maximum voltage shock of the circuit system, the suitable clamp voltage is selected.

5. Ensure that the ESD device meets or exceeds the IEC 61000-4-2 level4.

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