Simple multi-protocol isolator interface circuit design

7050 OSC seed vibration

Photocoupler

Usually the product design time is very tight, and the funds for new product design are not spare. But no matter what, we must design a robust system that can operate in harsh environments without increasing costs. In general, this would require galvanic isolation to protect sensitive control electronics from external inrush and transient inrush currents. If your design involves many industrial interfaces, then when you see an array of RS-485, RS-232, CAN and I2C signal isolators on the official website of major semiconductor manufacturers, you will find yourself into a candy. The kids in the store are just as excited. However, when you want the purchasing manager to approve the purchase of these products, he will immediately pour you a cold water: "Can't you use some of the existing standard components? No matter what method, use them?"

In the future, you can answer "no problem" with enthusiasm, because this article will introduce you to a small number of industrial interface circuits, almost all of which use only one standard isolator. Figure 1-4 shows a simplified schematic of the most common digital interface for industrial applications.

Figure 1 Isolated RS-485 bus interface

Figure 2 Isolated CAN bus interface

Figure 3 Isolated RS-232 line interface

Figure 4 Multi-master application isolated I2C bus interface