How to correctly select ESD d

Electronic products must comply with standards such as IEC61000-4-2. System designers use a variety of methods to ensure that products meet mainstream ESD standards, including housing design, circuit board design, component selection, and even software repair. Input and output are an important method (I/O) for protecting components used at critical circuit nodes such as connectors. ESD diode protection elements are commonly referred to as transient voltage suppressors (TVS).

Principles and application requirements of ESD electrostatic protection:

Many integrated circuits (ICs) may have sensitive inputs (such as ESD under stress) that are easily damaged when the input voltage is much higher than normal. The area between the normal operating voltage and the voltage that starts to damage the equipment is a safe overvoltage zone. There is a slight overlap between the safety overpressure area and the equipment damage area because if a large overpressure lasts only for a short time, the equipment may be able to withstand it, even if it is not in the safety overpressure area.

When an ESD event occurs, the task of the diode is to maintain the input voltage within a safe overvoltage range without affecting system performance. ESD diodes control the voltage at sensitive nodes, directing current to the location of electrostatic events to limit the voltage at sensitive nodes, and directing current to less sensitive nodes such as ground level. To achieve this function, ESD diodes must have a high impedance within the normal operating voltage range and a low impedance outside the normal operating voltage range, thereby directly drawing current from sensitive nodes and limiting transient voltages.

The basic requirements for ESD diodes are related to specific applications, but there are generally the following requirements:

(1) High impedance (low leakage) within the normal voltage range;

(2) Capacitance for the target application.

(3) Applicable conduction voltage;

(4) Able to work normally under expected electrostatic stress;

(5) During stress, it can quickly transition from high impedance to low impedance

(6) Low impedance outside the normal voltage range;

Classification of ESD diode devices

Before comparing specific TVS with device types, you need to understand two classifications.

Unidirectional and bidirectional protection: Unidirectional and bidirectional ESD diode devices can suppress positive and negative stresses. ESD diodes maintain a voltage range of high impedance and low leakage states, and it is best to understand the difference between these two terms. This voltage range determines the ESD circuit node type and can protect the device. ESD has symmetry compared to zero voltage diodes. Bidirectional diode. ESD is most suitable for protection voltages based on zero volt symmetric or bidirectional circuit nodes. ESD diode products have the characteristics of relative zero voltage asymmetry. ESD diode devices are suitable for protecting circuit nodes with consistently identical voltage polarity, such as unipolar voltages such as 0-5 volts.

Voltage positioning and arc elimination: The working principle of the voltage positioning device is to convert from a high impedance at low voltage to a low impedance at a higher voltage than the conduction voltage, and there is no negative impedance region (Figure 2). The device locates a voltage above the conduction voltage by providing a grounded low impedance channel. Arc cancellation (crowbar) When the voltage is low, the device also has a high impedance, but when the voltage is high, a new conductive mechanism is triggered, increasing the current and accompanying the voltage drop. Therefore, the arc suppression device has a negative impedance region.

The trigger voltage of some arc suppression devices may be high. When conducting electromagnetic compatibility tests, ESD electrostatic protection can often be provided even if the voltage has reached a level that may cause equipment damage if the arc cancellation TVS and trigger speed are fast enough. Arc suppression devices are sometimes referred to as "jerks" due to sudden voltage drops in equipment.