Working principle of transient voltage suppressor for directional diode

Working principle of transient voltage suppressor for directional diode
A. Types of transient voltage suppressors

Transient voltage suppressors can be classified into axial lead diodes, surface mount devices, and other styles based on their packaging and internal structure. Generally speaking, transient voltage suppressors with larger package sizes and higher power wattage (such as axial lead diodes, SMA/SMB package sizes, etc.) are mostly used in the power supply end of electronic systems or system interfaces with higher Surge specifications. To meet the design requirements of saving layout space on printed circuit boards (PCBs), R&D engineers often use surface mount technology transient voltage suppressors with multiple ESD protection ports. These surface mount transient voltage suppressors can provide multiple ESD protection ports in a small package, and they are often referred to as transient voltage suppressor arrays (TVS arrays or ESD suppressor arrays). The transient voltage suppressor array commonly used in the industrial sector, which can simultaneously provide 4 to 8 ESD protection ports, is the most commonly used for ESD protection in electronic systems.

The transient voltage suppressor array can be classified into high parasitic capacitance (CIN>3pF) and low parasitic capacitance (CIN<3pF) according to the transmission specifications of the output/input ports. High parasitic capacitance transient voltage suppressor arrays are mostly used for low transmission rate interfaces (such as SIM card I/O interfaces), while low parasitic capacitance transient voltage suppressor arrays are used for high transmission rate interfaces (such as USB interfaces).

B. Working principle of Steering diode TVS (Transient Voltage Suppressor)

The parasitic capacitance of ESD protection components is mainly determined by the PN junction of the semiconductor. In order to achieve optimal ESD protection capability, the size of the PN junction must be designed to be large enough, as larger PN junctions can cause an increase in parasitic capacitance. In order to achieve the best ESD protection effect under low parasitic capacitance conditions, it is necessary to achieve it through circuit design. To achieve this goal, the control diode architecture is the most commonly used design approach. 

As shown in Figure 1, the architecture of the directional diode transient voltage suppressor includes a clamping diode Dz connected to the power supply, and two diodes Dp and Dn connected to the output/input port and the power line/ground line. When the output/input port is subjected to a forward ESD surge, the ESD current IESD-1 is guided through diode Dp to the power line, and then through the clamping diode Dz between the power supplies to the ground line. When the output/input port is subjected to a negative ESD shock, the ESD current IESD-2 passes through the diode Dn in a forward direction to the ground line. Due to the fact that diodes can withstand high ESD currents under forward conduction conditions, the design size of Dp and Dn diodes does not need to be too large, and the parasitic capacitance generated is also relatively small; The size of the clamping diode Dz between power sources can be designed to be large enough to withstand high ESD currents, and the size of the clamping diode Dz does not affect the parasitic capacitance values of the output/input ports. The ESD protection component designed with this architecture can achieve low parasitic capacitance and high ESD protection capability.

C. Advantages of Steering Diode TVS Array

The array of transient voltage suppressors for directional diodes can provide multiple ESD protection ports on a small chip through chip layout design; The transient voltage suppressor array designed in this way has the following advantages:

Under low I/O parasitic capacitance conditions, ESD surge voltage will be clamped at a low voltage to prevent damage to the main chip.

2. Develop suitable packaging specifications for high-speed interface on printed circuit boards, making ESD layout design simpler.

3. Integrating multiple ESD protection interfaces onto a single chip can effectively reduce the production cost of transient voltage suppressor arrays for directional diodes. 

4. Some special circuits (such as reverse current blocking function) can be integrated into the chip of the transient voltage suppressor array of the control diode.

In recent years, the transmission specifications of various high-speed input and output interfaces have been continuously improved. Taking USB interface as an example, the transmission rate has increased from 480Mbps of USB 2.0 to 10Gbps of USB 3.1. These high-speed transmission chips all use advanced CMOS nanometer process technology, and the ability of these main chips to resist ESD has become very fragile; When developing the system, the application of TVS Array control diodes can help these main chips improve their tolerance to ESD.

Figure 2 shows the ESD protection circuit diagram of the directional diode transient voltage suppressor array applied to the USB 3.1 interface. The Dp and Dn diodes of the directional diode transient voltage suppressor array are designed in a smaller size to avoid parasitic capacitance affecting the normal operation of the main chip. The Dz diode should be able to clamp the ESD surge voltage as low as possible. A lower clamping voltage can ensure that the internal circuit of the main chip is not easily damaged by ESD surge voltage.

Table 1 summarizes the recommended parasitic capacitance specifications for ESD protection components for commonly used high-speed transmission interfaces. Due to different transmission specifications, the parasitic capacitance requirements for ESD protection components vary for high-speed transmission interfaces used in different applications.

Portable (or wearable) mobile devices have become very popular due to the rise of Internet of Things (IoT) applications. The development of these portable (or wearable) mobile devices by institutions is often aimed at designing them to be lightweight, thin, and short. For the ESD protection design of portable (or wearable) mobile devices, the application of a transient voltage suppressor array of directional diodes has the following advantages:

1. Save layout space on printed circuit boards

Due to the increasing popularity of portable (or wearable) devices, printed circuit boards must be made very small to meet the design goals of the system mechanism. The transient voltage suppressor array of directional diodes does not require a large amount of printed circuit board space and can provide ESD protection for multiple channels.

2. Reduce production costs

Figure 3 shows a printed circuit board using BAV99 and Zener diodes as ESD protection devices for the DVI interface; Figure 4 shows a printed circuit board with DVI (Digital Visual Interface) interface using a transient voltage suppressor array of directional diodes as an ESD protection device. From the design case of the printed circuit board with DVI interface in Figure 4, it can be seen that the number of transient voltage suppressors array for directional diodes used in DVI interface is much less than that of BAV99 and Zener diodes. This indicates that using a transient voltage suppressor array of directional diodes as an ESD protection device can help reduce the number of component devices used inside the electronic system, lower the production cost of the system, and improve the assembly speed of the system.

D. Conclusion

The transient voltage suppressor array of directional diodes is the best choice for ESD protection in high-speed transmission interfaces. The transient voltage suppressor array of directional diodes with low parasitic capacitance and low clamping voltage characteristics can help the main chip improve its tolerance to ESD. The transient voltage suppressor array of directional diodes has the following advantages:

1. Integrate multiple ESD protection ports onto a single ESD protection chip through chip layout design.

2. It can provide multiple packaging specifications and be applied to various high-speed input/output interface interfaces.

3. The transient voltage suppressor array of directional diodes can provide multi-channel ESD protection in a small package, achieving the goal of saving space for printed circuit boards; Helps reduce the number of component devices used within electronic systems, which can lower production costs and improve assembly speed.