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How should the unused pins be connected in a MBR3 CapSense design?
It is recommended that you connect the unused pins (configured in EZ-Click™, but not used) as per the Pinouts section in the MBR3 datasheet.
It is necessary that all pins in the controller are in a definite logic state regardless of the whether the pins are used in an application. When an unused Capsense pin which is a floating pin is left open, it could cause an input noise and lead to increased electromagnetic interference (EMI) and increased power consumption. These floating pins will act as antennas and becomes susceptible to electrical noises. This will most likely couple with your CapSense systems and would lead to erroneous results. Hence, it is recommended that you connect the unused pins to ground which will provide a better solution against noise.
But if the pin has AXRES functionality, then make sure that this pin is not connected to the ground during bootup. Otherwise, this will lead to resetting the device. Hence it is generally recommended that you connect the unused pin with AXRES functionality to VDD.
When the GPO pin’s drive mode is open drain, it is recommended to connect the pin to the ground. This will improve the overall grounding requirement of the chip and will make sure that the pin is not floating. If the drive mode of the GPO pin is strong drive, it is recommended to leave it open as it is internally driven down to logic 0. This helps in reducing EMI.
For unconfigured pins in EZ-Click, it is recommended to ground the unused pins to make the pins immune to noises.