RS485 transceiver realizes powerful lightning protection function - Power Circuit - Circuit Diagram

LC03-3.3 SOP8 TVS Static Protection 3.3V

Smart Grid is one of the most important energy-saving and carbon-reduction policies in the world. It has RS485 network for long-distance communication and is the key transmission interface in the smart grid. RS-485 transmission lines are usually placed outdoors or along cables, so it is often the case that lightning strikes cause transient interference on the transmission line and damage the device. In addition, the RS-485 network is generally a Party-Line (or Bus) structure, that is, one bus (Bus) connects tens to hundreds of RS485 transceivers (Transceiver). Therefore, a surge surge generated by a surge can cause damage to hundreds of RS-485 transceivers on the transmission line. Therefore, any voltage surge protection measures must be considered in the actual use of RS-485, and it is also an important measure to improve system reliability and safety. With the professional design experience in the ESD field, Jinghao Technology has launched the RS485 transceiver (AZRS3082) with IEC61000-4-5 (8/20μs) ±30A lightning strike function. The AZRS3082 is the most powerful lightning protection function on the market. RS485 transceiver.

AZRS3082 has the most powerful ESD protection

In the traditional RS485 transceiver, in order to comply with the DL/T 645 standard, the transmission line interface A, B will have HBM 15kV specifications at both ends, but in practical applications, such protection is not enough. Therefore, the current general solution is to add a transient voltage suppressor (TVS) to the outside of the RS-485 receiver to prevent voltage surges, but the general TVS is difficult to achieve high power, so the lightning wave When the surge comes, the instantaneous large energy will directly damage the general TVS. Especially the TVS integrated into the chip is more fragile, so it is necessary to add a lightning surge protection component.

At present, the additional lightning surge protection components include gas and ceramic discharge tubes, varistor and TVS. The current resistance of the discharge tube is very strong, but its reaction speed is slow, and the clamping potential is also very high (about 800V). This kind of characteristic makes its protection effect greatly reduced. It is often encountered that even if a discharge tube is added, the protected component is still Will damage. The varistor has large parasitic capacitance, high on-resistance, and low voltage varistor leakage current, and is not suitable for RS-485 interface protection. TVS, which is traditionally made of semiconductors, has a very fast response speed, but its ability to withstand high voltage and high current is insufficient, so it is difficult to withstand the impact of lightning surges.

Dr. Chen Zhihao from Jingsheng Technology pointed out: "Shenzhen Technology Co., Ltd. is aiming at developing high-reliability and high-security interface transmission ICs, in order to make the design of system customers simpler and more efficient. Dr. Chen further pointed out: "TVS with powerful lightning protection is generally not easy to integrate into traditional CMOS ICs, but Crystal Technology has overcome the bottleneck of many technologies by holding the background of ESD professional design. ! 』. The two-way characteristics of the Transmission-Line-Pulse (TLP) with built-in special TVS are shown in Figure 1. A comparison of the test characteristics of the lightning surge with the built-in lightning protection receiver of his home is shown in Figure 2. It can be seen from the figure that the AZRS3082 can not only withstand higher lightning surge current, but also has a lower surge voltage (Surge Clamping Voltage). When the voltage of the TVS lightning strike clamp is lower, the protection effect on the chip will be better. .

The built-in special TVS RS485 transceiver also provides system-level electrostatic discharge protection, which makes the transmission line interface A and B terminals more fully protected. The ESD specifications of the RS485 transmission terminals A and B are as follows:

1. IEC 61000-4-2, Contact Mode Contact Discharge ±30 kV

2. IEC 61000-4-2, Air Discharge Mode Air-Gap Discharge ±30 kV

3. IEC 61000-4-2, Electronic Fast Pulse Mode EFT (5/50ns) 4.4 kV

4. IEC 61000-4-5, lightning surge Surge (8/20μs) ±30 A

In addition to the transmission end A, B has complete ESD protection, the AZRS3082 has built-in overall protection, and the Human Body Model (HBM) electrostatic discharge protection is DL/T 645 (JEDEC human body model HBM 15kV) for each PIN pin. The chip ESD protection architecture is shown in Figure 3. In addition, for industrial applications, the Machine Model (MM) tests up to 800V, making it the most secure in Profibus (Industrial Automation) applications. In terms of chip self-protection, the AZRS3082's Charge Device Model (CDM) protection capability is as high as 2kV, which makes the chip self-protective due to excessive charge accumulated in the process environment. In terms of stability and reliability, the AZRS3082 has a latch-up immunity of up to 400 mA, so it can be used in a noisy environment.

Figure 1 AZRS3082 chip built-in lightning protection TVS TLP bidirectional curve.