Electrostatic discharge (ESD) is common in daily life and poses a serious threat to electronic devices; products that are often in contact with the human body are more vulnerable to electrostatic impact. This article will introduce you to the generation of static electricity and its influence on electronic products, as well as the selection of anti-static components.
Diversified ESD protective devices meet different application requirements
What is ESD? ESD is the release of static electricity when two objects come into contact. ESD generated from the human body can be several thousand volts, and when the high voltage pulse enters a touched electronic device, it will cause the failure or destruction of the IC inside. In order to prevent product or system damage caused by ESD intrusion into the touched electronic device, it is necessary to install corresponding components to inhibit or eliminate ESD.
That is to adopt ESD countermeasures at all points which may come into contact with the human body or other objects of the electrical device.
Examples include USB2.0, USB3.0, output terminal, LAN, or other points where a user connects or disconnects a connector, as well as cases where an operation button of an electronic product needs to be touched, or cases where a device comes into contact with a circuit board during production, and cases where the circuit boards are connected to each other using a connector. Components installed at these points as ESD countermeasures are called “ESD protective devices”.
Electronic device manufacturers need to formulate appropriate ESD countermeasures to meet the standards of each electronic equipment, and devise various tests and standards for various purposes and products. At present, there are three representative testing methods for various devices such as IC and electronic components, including HBM (Human Body Model), MM (Machine Model) and CDM (Charged Device Model). Under applicable test conditions, each item in these tests will be carried out on applicable components and devices according to these standards.
ESD protective devices need to pass the test before leaving the factory, and their test specifications are contained in the standard IEC61000-4-2. During the test, 150pF capacitor and 330 Ω internal resistor will be included in the circuit, and the products are exposed to four ESD voltages in the order of 2kV, 4kV, 6kV and 8kV, so as to evaluate the breakdown resistance and further understand the conditions of these devices.
The main function of ESD protective devices and countermeasure components is to enable ESD entering the devices to escape to the ground. If there is no protective device, ESD with a voltage of several thousand volts will directly act on the internal IC, which will have a serious impact on the chip.
When an ESD protective device is installed between the external interface and the IC to protect the IC, the input of the IC will be grounded through the ESD protective device, allowing ESD to escape to the ground. Under normal driving voltage (several volts), the IC is isolated from ground, so data communication will not be impaired. When a voltage of several thousand volts is applied, the IC is grounded, and when a voltage of several volts is applied, it is isolated from ground, which is a necessary function of ESD protective devices.
ESD protective devices differ from each other in respect of principle of operation and raw material, in order to realize the necessary function. EDS protective devices are broadly classified into ceramic base and semiconductor base types employing silicon or a polymer as the raw material. Ceramic base types are divided into two kinds, a varistor type which employs a voltage-dependent variable resistor, and an inter-electrode discharge suppressor type. Semiconductor base types include a Zener (constant voltage) diode type and field effect transistor method.
Murata is an expert in manufacturing ESD protective devices and offers both ceramic base and semiconductor base type ESD protective devices. These include the LXES A series based on the ceramic base types using the inter-electrode discharge technology, and the LXES T series based on the semiconductor base types using the Zener (constant voltage) diode type and field effect transistor method.
The ESD protective devices offered by Murata use a mechanism called an “inter-electrode discharge method”. These products are of a construction such that the internal electrodes face each other in both directions. Normally, the electrodes are isolated, but when a high voltage is applied, a discharge occurs between the internal electrodes, causing current to flow to ground.
A semiconductor base ESD protective device uses a mechanism called a Zener diode method. A Zener diode consists of a combination of a P type semiconductor (condition in which there is a deficiency of electrons) and an N type semiconductor (condition in which there is an excess of electrons). A silicon base ESD protective device utilizes the technology of this diode to pass current to ground when an overvoltage (ESD) exceeding the breakdown voltage is applied.
Even if the range of applications is limited to electronic and electrical devices that are used in daily life, the range of places where ESD protective devices is used is diverse. In addition, the adoption of appropriate ESD countermeasures leads to stable performance of the device. Murata’s ESD protective devices have high performance and reliability. We offer a full lineup of products that can be used for a variety of devices and applications.
Murata manufactures a wide range of ESD protective devices, including special devices for high-speed communication, ultra-small devices and products with integrated noise filters. These devices can also be used to replace varistors, Zener diodes (TVS) and suppressors. The product line includes LXES A series made of ceramic, LXES T series ESD protective devices made of silicon, and LXES D series integrated by ESD protective devices and common mode choke coil, which can provide customers with diversified choices.