Application note published for interference suppression

Würth Elektronik has published a new Application Note: "ANP121 – Filter and surge protection for I²C-Bus". In this new note, the supplier provides practical support to developers utilising the I²C bus in cross-circuit-board scenarios. An extension of the interface through connectors or cables can, however, potentially make the I²C bus exposed to external interference such as ESD, burst, and radiated RF. This Application Note aims to offer a suitable filter and protection circuit that improves the noise immunity of the I²C bus without compromising the signal quality of the data and clock lines.

The latest addition to the collection of application-specific tips on the company's support sites comprises the sections "Overview I²C bus ", "Overview I2C specifications"," Selection of the filter and overvoltage protection components", "LTspice simulation with 400kHz clock rate ", and "Measurement of a real application with 400kHz clock rate ". The Application Note was developed by building simulation models in LTspice and measuring them in a real-life application to verify the simulation results.

Extra measurements were made on the company's SensorBLE FeatherWing kit to verify the simulation. This kit comprises a master board with a microcontroller, two other boards fitted with a WE Bluetooth module, and a FeatherWing system with WE sensors (three-axis acceleration, temperature, humidity, pressure). The master board communicates with the other two boards via I²C bus at a maximum data rate of 400kBit/s. A 20cm (7.87") long data cable connected the sensor board to the rest of the I²C. A parasitic capacitance of 400pF with respect to GND was simulated utilising MLCCs. The simulation and measurement revealed that SMT multilayer ferrites in combination with ESD protection diodes have practically no effect on the data signal (SDA) and the clock signal (SCL) of the I²C bus, but rather improve the noise immunity of the I²C bus.