Protecting the I2C bus: Effective Filtering and Surge Protection

I2C, or inter-Integrated circuit, is an efficient and well-defined communication protocol designed to connect a microcontroller with peripheral ICs, such as sensors or memory devices.? It allows communication with up to 127 devices over just two wires (data or SDA and clock or SCL). This simplicity can be very appealing, especially when attempting to reduce the number of signal wires or when limited on microcontroller pins. However, it can become problematic in real world scenarios when several devices share the same bus, especially when the I2C bus is extended into other areas through connectors and cables. If you are reading this, chances are you’ve ran into these I2C issues as well, but Würth Elektronik is here to help.??

In a recent application note from Würth Elektronik titled “Filter and Surge Protection for the I2C bus,” methods to protect the I2C bus from external interference without sacrificing signal quality are outlined and tested. Here are the key takeaways.

Selecting the Right Pull-Up Resistors?

The correct selection of pull-up resistors is essential for proper I2C bus operation. Pull-up resistors are required on both SDA (data) and SCL (clock) to ensure the lines are pulled to a known high state when not actively driven low by devices on the bus. Selecting the appropriate resistor values is critical for balancing signal integrity and power consumption. The mathematical relationship of the min./max values for the pull-up resistors is as follows:?

Surge Protection and EMI Filtering?

To protect the I2C bus from voltage surges and electromagnetic interference, a combination of ferrite beads and transient voltage suppression (TVS) diodes is recommended. Ferrite beads are particularly effective at filtering out high-frequency noise that can disrupt communication on the I2C lines. Würth's WE-CBF wide band SMT ferrite beads, for example, continuously build up impedance above 10 MHz and are therefore able to protect the bus against high-frequency interference.?

For surge protection, TVS diodes are used to clamp high-voltage spikes and protect the bus lines from transient events such as electrostatic discharge (ESD). These diodes act as voltage limiters, safely redirecting excessive energy away from sensitive I2C components. Würth Elektronik offers a range of TVS diodes designed for various voltage levels, ensuring comprehensive protection for I2C systems operating in harsh environments.?

Conclusion?

Implementing robust filtering, surge protection, and selecting the appropriate pull-up resistors are essential for maintaining the integrity and reliability of I2C communication systems. By incorporating ferrite beads, TVS diodes, and optimizing pull-up resistors, engineers can significantly reduce the impact of ESD, burst and radiated RF, ensuring correct signaling for I2C bus lines. The solutions highlighted in this application note can be adapted to various applications, making them a versatile choice for improving the robustness of I2C buses.?

For more detailed guidance, Würth Elektronik's application note provides in-depth recommendations and product suggestions to help you design with confidence in environments prone to EMI and surges.?