How much do you know about ESD protection tubes?

1,6682019-01-04

Static electricity is a universal natural phenomenon that everyone is very familiar with. Although the unique characteristics and functions of static electricity are applied to our daily life, such as: electrostatic dust removal, electrostatic copying, electrostatic spraying, electrostatic flocking, electrostatic separation, etc., electrostatic discharge is a hazard to electronic products and equipment. , Resulting in dysfunction or even damage to some precision devices. For this reason, the interference caused by static electricity on the circuit and the damage to the components, CMOS circuits and interface circuits have attracted attention. In particular, engineers who have been exposed to the design of electrostatic protection solutions know the degree of interference or damage caused by static electricity to electronic products. For this reason, in the circuit design, ESD protection diode is an indispensable circuit protection device.

ESD Device Overview

ESD, Chinese meaning: Electrostatic discharge. The internationally used equipment for electrostatic protection is collectively referred to as “ESD”. It is a commonly used overvoltage and electrostatic protection component to protect sensitive circuits in electronic equipment from electrostatic influence. The ESD protection tube is connected in parallel to the circuit. When the circuit is operating normally, the ESD protection tube is in a high-impedance state, which does not affect the normal operation of the line. When the circuit has abnormal overvoltage and breakdown voltage, it quickly changes from a high-impedance state to a low-impedance state. Provide instantaneous current to provide an impedance conduction path, and clamp abnormal voltage to a safe level, thereby protecting the protected IC or line.

ESD diodes are widely used in USB interfaces, due to their unique advantages such as small size, diversified packaging, fast response time (less than 1ns), low capacitance value, low leakage current (less than 1uA), ultra-low clamping voltage, and low voltage value. HDMI interface, antenna interface, VGA interface, IEEE1394 interface, DVI interface, key circuit, SIM card, headset and various data transmission interfaces.

Selection of ESD electrostatic diode:

The selection of ESD electrostatic protection diodes is one of the most questions asked by almost every buyer, and it is also a headache. Before selecting the ESD diode, you need to be familiar with the parameters and characteristics of the ESD protection tube, follow the selection formula of the electrostatic protection component, and also select the appropriate ESD electrostatic protection diode according to the design requirements of the scheme.

First, use Array-type ESD protection components so that the PCB space can be reduced and the parasitic impedance of the PCB can be reduced with the minimum number of components;

Second, the line capacitance of the ESD protection component must be low enough. For example, USB2.0 needs to use less than 3pF, USB3.0 needs to use less than 0.3pF, and 10 / 100M LAN needs to use ESD protection components less than 3pF;

Third, the clamping voltage of ESD protection components must be low enough to allow the system to operate undisturbed when ESD occurs. As for how low the clamping voltage is enough, it depends on the system’s noise immunity.