Xbee 3 Cellular USB pins best practices

New design, need to use the i2c. But from the documentation pin 7, I2C_SDA is also USB D+.

The application is intended to have a minimal footprint, but it needs to be possible to update it.


  1. Don’t install a USB connection, just rely on Over-the-Air updates from DRM or remove the part to update it in a dev kit.

  2. Provide a jumper or switch to allow USB when needed, disabling the i2c during update. If the USB interface needs to operate at High Speed this will be an issue for the layout, too many antenna traces.

What is the best practice in this situation?

Option 2 is the best option.

I notice on the XBIB-CU-TH dev board they just use a DIP switch.

A violation of matched pair impedance rules for USB. Probably they are using the old USB 1.0/Low Speed standard and it doesn’t really matter.