Low-Cost, High-Speed I2C Isolation with Digital Isolators

Many articles have been published using opto-couplers for I2C isolation. These circuits are somewhat complex, sensitive to bus capacitance, and limited in speed. They are also not compatible with high-speed digital isolators having standard CMOS input levels.

This application note shows how to convert a standard Si8442 high-speed digital isolator to a bidirectional I2C isolator. In addition to being compatible with digital isolators, the circuit is simpler than previously published solutions, completely insensitive to bus capacitance, and can easily support the standard 400 kHz maximum I2C bus rate.