Driving I2C-Bus Signals Over Twisted Pair Cables with PCA9605
The availability of powerful I2C buffers that drive their I/Os on both sides to a nominal ground or ‘zero offset’ logic level allows the removal of noise introduced into one section of a larger bus system. That ‘regeneration’ of clean I2C signals enables building long I2C buses by combining together relatively short bus sections, each say less than 20 meters, using such buffers or multiplexers that contain them. Conventional twisted pair communication cabling with its convenient connectors, and a ‘modular’ I2C system approach, make large system assembly easy. Each drop point or node can be individually selected for bidirectional data communication with the Master just by using normal I2C software addressing. As an example, a system is described for control of LED lighting displays and it is suggested that the power for the LEDs, and the I2C control system, might be economically provided using ‘extra low voltage’ distribution at 48 V using either the control signal cable or similar low cost wiring in a manner similar to that used in ‘Power over the Ethernet’ systems. The simplicity and flexibility of this approach makes it attractive to consider as an alternative to other control systems such as RS-485 or CAN bus.
Summary
This NXP application note explains how the PCA9605 I2C bus buffer enables reliable, long-distance I2C links by regenerating zero-offset signals and allowing bus segments to be connected over conventional twisted-pair cabling. It shows practical system architectures, wiring and termination considerations, and a real-world LED lighting control example to help engineers design modular, extendable I2C networks.
Key Takeaways
- Describe how the PCA9605 regenerates I2C signals to remove offset and noise between bus segments.
- Design a segmented I2C network over twisted-pair cable, including node drops and addressing for modular expansion.
- Calculate appropriate pull-up resistor values and evaluate bus capacitance and segment length limits for reliable operation.
- Implement wiring, termination, and grounding practices to minimize EMI and ensure signal integrity across long runs.
- Apply the approach to real systems (for example LED lighting control), selecting appropriate components and topologies for robust communication.
Who Should Read This
Embedded firmware or hardware engineers (intermediate level) designing or extending I2C networks for distributed sensors, actuators, or lighting systems who need practical guidance on long-distance bus design.
Still RelevantIntermediate
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