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

LC03-3.3 SOP8 TVS Static Protection 3.3V

The Smart Grid stands as one of the most crucial energy-saving and carbon-reduction strategies globally. It employs an RS485 network for long-distance communication, making it a pivotal transmission interface within the Smart Grid system. Given that RS-485 transmission lines are typically installed outdoors or alongside cables, they are frequently exposed to transient interference caused by lightning strikes, which can damage devices. Additionally, the RS-485 network usually adopts a Party-Line (or Bus) configuration, meaning one bus (Bus) can connect dozens to hundreds of RS485 transceivers (Transceiver). Consequently, a surge generated by lightning could potentially damage hundreds of RS-485 transceivers on the transmission line. Therefore, considering any form of voltage surge protection is essential in the practical application of RS-485, and it is also a significant step toward enhancing system reliability and safety. Drawing upon extensive expertise in the ESD field, Jinghao Technology has introduced the RS485 transceiver (AZRS3082) featuring an IEC61000-4-5 (8/20μs) ±30A lightning strike function. The AZRS3082 boasts the most robust lightning protection capabilities among RS485 transceivers available on the market.

The AZRS3082 offers unparalleled ESD protection. In conventional RS485 transceivers, to meet the DL/T 645 standard, the transmission line interfaces A and B would typically have HBM 15kV specifications at both ends. However, in real-world applications, this level of protection is often insufficient. Thus, the current common approach involves adding a transient voltage suppressor (TVS) externally to the RS-485 receiver to guard against voltage surges. However, most general-purpose TVS devices struggle to handle high power, so when a lightning surge hits, the sudden large amount of energy can easily damage these TVS components. Particularly, TVS integrated into chips tends to be more fragile, necessitating the addition of a dedicated lightning surge protection component.

Presently, the supplementary lightning surge protection components include gas discharge tubes, ceramic discharge tubes, varistors, and TVS. The current resistance of discharge tubes is strong, yet their reaction time is slow, and their clamping potential is quite high (approximately 800V). These characteristics significantly reduce their protective efficacy. Often, even after adding a discharge tube, the protected component may still get damaged. Varistors possess large parasitic capacitance, high on-resistance, and low leakage current at low voltages, making them unsuitable for RS-485 interface protection. Traditional semiconductor-based TVS devices respond quickly, but their ability to withstand high voltage and high current is limited, making them ill-suited for handling lightning surges.

Dr. Chen Zhihao from Jinghao Technology remarked: “Shenzhen Technology Co., Ltd. is committed to developing high-reliability and high-security interface transmission ICs, aiming to simplify and enhance the efficiency of system customer designs.” Dr. Chen further emphasized: “TVS with robust lightning protection is generally challenging to integrate into traditional CMOS ICs. However, Crystal Technology has overcome numerous technological hurdles through its expertise in ESD professional design!” The bidirectional characteristics of the built-in special TVS Transmission-Line-Pulse (TLP) are illustrated in Figure 1. A comparison of the lightning surge test characteristics of the built-in lightning protection receiver at his company is shown in Figure 2. As seen in the figures, the AZRS3082 can endure higher lightning surge currents while maintaining a lower surge voltage (Surge Clamping Voltage). The lower the TVS lightning strike clamp voltage, the better the protection effect on the chip.

The built-in special TVS RS485 transceiver also provides system-level electrostatic discharge protection, ensuring comprehensive protection for the transmission line interface A and B terminals. The ESD specifications for 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 (8/20μs) ±30 A

Besides providing full ESD protection at the transmission end A and B, the AZRS3082 also features overall protection, offering Human Body Model (HBM) electrostatic discharge protection for each PIN pin, meeting the DL/T 645 (JEDEC human body model HBM 15kV) standard. The chip's ESD protection architecture is depicted in Figure 3. Furthermore, for industrial applications, the Machine Model (MM) tests reach up to 800V, making it the safest choice for Profibus (Industrial Automation) applications. In terms of chip self-protection, the AZRS3082's Charge Device Model (CDM) protection capability is as high as 2kV, protecting the chip from excessive charge accumulation during processing. Regarding stability and reliability, the AZRS3082 exhibits a latch-up immunity of up to 400 mA, enabling its use in noisy environments.

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