Qwiic Differential I2C Bus Extender (PCA9615) Hookup Guide

Contributors: Joel_E_B, Alex the Giant

Hardware Assembly

Ethernet cables used must be straight-through (i.e. Pin 1 on one side of the cable is connect to pin 1 on the other side. The same for pin 2 and so on.).

I²C Pull-Up Resistors

Remember, each individual non-differential I²C bus needs at least one set of pull-up resistors enabled. Make sure you keep track of which devices have their I²C pull-ups enabled and which do not.

Power Schemes

With two power supply rails and quite a few jumpers, it's easy to feel confused about how to power the differential I²C bus extender. In this section, we'll go over the different ways you can power your project.

VDD_A == VDD, Power Whole Bus (Default)

• VDD_A and VDD_B are connected.
• Both are powered at 3.3V.
• Power is connected to a twisted pair of the Ethernet cable and sent to the peripheral nodes.
• No power is required at the peripheral nodes.

VDD_A != VDD_B, Power Whole Bus

• VDD A-B jumper trace has been cut.
• Separate power supply (3.0-5.5V) is supplied to VDD_B, while VDD_A remains at 3.3V.
• VDD_B voltage is connected to a twisted pair of the Ethernet cable and sent to the peripheral nodes.
• No power is required at the peripheral nodes.

VDD_A == VDD_ B, Power Each Node Separately

• VDD_A and VDD_B are connected.
• Both are powered at 3.3V.
• Jumpers underneath board (VDDB and GND) are cut and power is NOT connected to the Ethernet cable.
• Each peripheral node is powered individually with 3.3V only. Differential I²C signals are the only connections on the bus.

VDD_A != VDD_ B, Power Each Node Separately

• VDD A-B jumper trace has been cut on the top of the board.
• Separate power supply (3.0-5.5V) is supplied to VDD_B, while VDD_A remains at 3.3V.
• Jumpers underneath board (VDDB and GND) are cut and power is NOT connected to the Ethernet cable.
• Each peripheral node is powered individually with 3.3V only. Differential I²C signals are the only connections on the bus.

VDD_A == VDD_ B, Power Whole Bus (Non-Qwiic Option)

• VDD_A and VDD_B are connected.
• Both are powered at 5V.
• Power is connected to a twisted pair of the Ethernet cable and sent to the peripheral nodes.
• No power is required at the peripheral nodes.

VDD_A == VDD_ B, Power Each Node Separately (Non-Qwiic Option)

• VDD_A and VDD_B are connected.
• Both are powered at 5V.
• Jumpers underneath board (VDDB and GND) are cut and power is NOT connected to the Ethernet cable.
• Each peripheral node is powered individually with 5V only. Differential I²C signals are the only connections on the bus.