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

LC03-3.3 SOP8 TVS Static Protection 3.3V

Smart Grid represents one of the most critical energy-saving and carbon-reduction strategies globally. It features an RS485 network for long-distance communication, serving as the key transmission interface within the Smart Grid system. However, due to its placement outdoors or along cables, RS-485 transmission lines are frequently exposed to transient interference caused by lightning strikes, potentially damaging connected devices. Furthermore, the RS-485 network typically employs a Party-Line (or Bus) configuration, where a single bus connects dozens to hundreds of RS485 transceivers. Consequently, a surge event could lead to widespread damage across multiple transceivers on the same line. Therefore, incorporating effective voltage surge protection is essential when using RS-485, and it remains a crucial step toward enhancing system reliability and safety. Drawing on extensive expertise in ESD design, Jinghao Technology has introduced the AZRS3082 RS485 transceiver, equipped with IEC61000-4-5 (8/20μs) ±30A lightning protection capabilities. The AZRS3082 stands as the most robust lightning protection solution available for RS485 transceivers.

The AZRS3082 boasts unparalleled ESD protection. Traditional RS485 transceivers meet the DL/T 645 standard by providing HBM 15kV specifications at both ends of the transmission line interfaces A and B. However, this level of protection proves insufficient in real-world applications. Hence, a common approach involves adding an external transient voltage suppressor (TVS) to the RS-485 receiver to counteract voltage surges. Yet, typical TVS components struggle to handle high power, leaving them vulnerable to damage when subjected to intense lightning surges. Integrated TVS chips are particularly susceptible to failure under such conditions, necessitating additional surge protection components. Current options for supplementary surge protection include gas discharge tubes, ceramic discharge tubes, varistors, and TVS diodes. While discharge tubes exhibit high resistance, their slow response time and high clamping voltages (around 800V) severely limit their protective effectiveness. Even with the inclusion of a discharge tube, the protected components may still sustain damage. Varistors suffer from large parasitic capacitance, high on-resistance, and low leakage currents at lower voltages, making them unsuitable for RS-485 interface protection. Traditional semiconductor-based TVS devices offer rapid response times but lack the capacity to endure high voltage and current levels, rendering them inadequate for withstanding lightning surges.

Dr. Chen Zhihao from Jingsheng Technology remarked, “Shenzhen Technology Co., Ltd. focuses on developing high-reliability and high-security interface transmission ICs, simplifying system design for customers while boosting efficiency.” He continued, “Integrating a highly capable TVS for lightning protection into conventional CMOS ICs presents significant technical challenges. However, Crystal Technology has successfully overcome these hurdles by leveraging its ESD design expertise.” As illustrated in Figure 1, the bidirectional characteristics of the built-in special TVS in the Transmission-Line-Pulse (TLP) demonstrate superior performance. A comparison of the lightning surge test results between the AZRS3082 and similar products from other manufacturers is depicted in Figure 2. From the figures, it is evident that the AZRS3082 can withstand higher lightning surge currents while maintaining a lower surge voltage (Surge Clamping Voltage). Lower TVS clamping voltages enhance the protective efficacy of the chip. Moreover, the integrated special TVS ensures comprehensive system-level electrostatic discharge protection, safeguarding the transmission line interfaces A and B more comprehensively.

The ESD specifications for the RS485 transmission terminals A and B are as follows:

• IEC 61000-4-2, Contact Mode Contact Discharge ±30 kV
• IEC 61000-4-2, Air Discharge Mode Air-Gap Discharge ±30 kV
• IEC 61000-4-2, Electronic Fast Pulse Mode EFT (5/50ns) 4.4 kV
• IEC 61000-4-5, Lightning Surge (8/20μs) ±30 A

In addition to offering complete ESD protection at the transmission end A and B, the AZRS3082 provides comprehensive internal protection. Each pin adheres to the Human Body Model (HBM) electrostatic discharge protection standards set by DL/T 645 (JEDEC human body model HBM 15kV). The chip's ESD protection architecture is outlined in Figure 3. For industrial applications, the Machine Model (MM) tests reach up to 800V, ensuring maximum security in Profibus (Industrial Automation) environments. In terms of chip self-protection, the AZRS3082's Charge Device Model (CDM) protection capability reaches 2kV, safeguarding the chip against excessive charge accumulation during processing. Regarding stability and reliability, the AZRS3082 exhibits a latch-up immunity of up to 400 mA, enabling reliable operation in noisy environments.

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

Overall, the AZRS3082 RS485 transceiver represents a breakthrough in lightning surge protection technology. Its integration of advanced ESD and lightning protection features makes it an indispensable component in modern Smart Grid systems. By addressing the limitations of traditional surge protection solutions, Jinghao Technology has delivered a product that combines reliability, durability, and cutting-edge design, setting a new benchmark in the industry.