How to tell one type of TVS from another

Transient Voltage Suppressor, or TVS, is transistor-type high-performance protection element. TVS is used to protect rear ICs from accidental overvoltage and overcurrent ESD or EOS fluctuation. Its working principle is provided in Fig. 1: first, with the reverse breakdown capability of TVS transistor, TVS turns high impedance between two poles into low impedance in 10-12 seconds (ps) when it is subject to transient high-energy impulses. It absorbs large irregular ESD/EOS energy and dumps it into earth, thus keeping the clamping voltage between two poles at the predefined level. This protects the precision elements in electronic circuitry effectively from damage due to irrational impulses, which makes TVS a very common protection element in electronics. 

Figure 1 How the TVS protects system

TVS types

1.        By the magnitude of power, there are high-power TVSs and low-power TVSs. 

 High-power TVSs are used mostly in power supply systems to protect against high-energy surges. They are used in, for example, industrial equipment, automotive electronics, and aerospace electronics. High-power TVSs have a capacitance up to hundreds of pF with a response rate < 1ns. Their packaging is relatively large since they have to resist the impact of excessive energy. The packaging is mostly SMA or higher and features kW-level surge resistance. At present, the high-power TVSs are defined industrially as those of 3000W or greater. The TVS transistor SM series for automotives feature5.5As a peak impulse power of 6600W, making them high-power TVSs. Currently for high-power TVSs, the withstanding test criterion is 10/1000uS for single units. Low-power TVSs are mainly used for ns-level waveform impulses, such as ESD or EFT. They are commonly used in signal wiring and power supply protection. The elements are not designed into large package for high-power design, as they are used primarily for protection against low-energy impulses. 25AFor low-power TVSs, the package can be 0402, 0201 or even smaller like 01005. The feature is that the parasitic voltage can be at pF level or lower, and that’s why these elements are suitable and widely used for high-speed signals. It is normal in low-power TVSs that the withstanding test is performed according to IEC61000-4-2. In case of issues with electrostatic discharge or ESD, a low-power TVS is usually added to a sensitive circuit or the path where external signals run through, as to release the ESD.   

 2.        By application, there are universal TVSs and dedicated TVSs. 

Universal TVSs are those that are without specific certification or specifications, and can be used extensively in all kinds of electronics; while dedicated TVSs are those with normal specifications and additional specific certification. For example, there are TVSs with AEC-Q101 certification for automotive applications, and the reliability test is more rigorous. For the TVS production lines of Amazing Microelectronic, the AZ9 series is for automotive application and the entire series has been certified for AEC-Q101. Other series are mostly universal TVSs that are ESD/EOS protection solutions designed for all electronic products. As shown in Fig. 2, Amazing Microelectronic provides a wide range of TVS products, more than 400 models; for example, the AZ1 is designed specifically for high-speed transmission interfaces. It features the snap-back technique in SCR in the COMS process, giving it the ability to keep the clamping voltage within a smaller but more reasonable range thanks to smaller parasitic capacitance. 

Figure 2 TVS protection lines of Amazing Microelectronic

3.        By voltage, there are high-voltage TVSs and low-voltage TVSs. 

 There are chip-level power supply and system-level power supply when it comes to the type of power supply for electronic systems. As the name suggests, the chip-level power supply powers chips with the voltage ranging no more than 5V in general. For example, the voltage of a normal digital signal is 3.3V or 5V, and that of chip-level power supply is 3.3V or 5V. with the extensive applications of high-speed signaling, a lower signaling voltage is needed to reduce power consumption and EMI due to voltage swing. That’s why the core voltage of mainstream high-speed interface chips is lower than 3.3V at, for example, 2.5V, 1.8V, 1.2V or even lower. The TVSs corresponding to chip-level power supply are generically called low-voltage TVSs with working voltage ≦5V. On the other hand, system-level power supply usually features voltage >5V typically, and powers power management chips. Commonly, the power voltages are 9V, 12V and 24V. The input power is reduced to chip-level power through power chips like DCDC. As shown in Fig. 2, Amazing Microelectronic’s AZ4 series is a high-voltage TVS series with the maximum working voltage up to 100V. Figure 3 below lists some of Amazing Microelectronic’s high-voltage models.Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book.

Figure 3 Amazing Microelectronic’s high-voltage TVS models

4.        By number of channels, there are single-channel TVSs and multi-channel TVSs.

Transistors are traditionally one-way PN transistors with a package featuring a single channel and two leads. Also traditionally, a TVS comes with a single-channel package, similar to that of transistors. Single-channel TVSs features small package for flexible PCB layout. However, if single-channel TVSs are to be used in an interface dealing with sophisticated and complicated signals, such as HDMI and Type-C, there will be too many TVSs occupying precious space and result in higher overall production costs. This is where multi-channel TVSs come in, as they can be integrated into a rich and more advanced protection circuit in its chip-level package, providing 2 or more protected channels. The multi-channel TVS array developed by Amazing Microelectronic is a semiconductor process element with a single chip inside; this indicates how multiple ESG protection ports are integrated in a tiny chip via chip layout design. It features small capacitance and fast conduction, and provides enough maintaining voltage to prevent latch-up in system based on the voltage applications. A multi-channel TVS array can be designed with a lower and safer clamping voltage, meaning that the ESD/EOS surge voltage is clamped to a lower value, thus protecting electronic systems from ESD/EOS surges. Also depending on the end applications, packages with various sizes are available, including SOT23, SC70 and DFN. Thanks to the small space needed on PCB, multi-channel TVSs are often seen on small-sized PCBs. Figure 4 provides a comparison of single-channel TVS vs. multi-channel TVS array. 

Figure 4 Single-channel TVS vs. multi-channel TVS array

5.        By direction, there are one-way TVSs and two-way TVSs. 

There are one-way and two-way TVSs. A one-way TVSs works similarly to a transistor, whereas a two-way TVS is like two transistors connected reversely in series. One-way TVSs are generally used in DC circuits or digital signaling, while two-way TVSs are suitable for AC circuits or analogue signaling. As shown on the left in Fig. 5, the positive properties of a one-way TVS are the same as those of a typical transistor. The nearly “perpendicular” breakdown at the reverse breakdown flection point is a typical PN-node avalanche. As indicated by the curve section corresponding to the values from breakdown point to clamping voltage, the TVS current spikes rapidly when a transient over-voltage impulse strikes, and the reverse voltage increases to clamping voltage and stays at this level, while the forward voltage of TVS falls between 0.8V and for 0.9V for silicone material, depending on the PN-node material. After forward conduction, the current increases exponentially, while the forward voltage stays at the clamping voltage value. On the right in Figure 5, the I-V curve of two-way TVS looks like 2 one-way TVSs standing “back to back.” The same avalanche breakdown and clamping characteristics are observed in both the forward and reverse directions. The interfering voltage added to either end will be suppressed immediately once it exceeds the clamping voltage. The two-way TVS is a convenient solution for AC circuits and analogue signaling. 

Figure 5 I-V curves, one-way TVS vs. two-way TVS