What is the correct connection of pin 5 of the Si446x RF chips? GND or NC?
It is recommended to connect this pin to GND per our reference design schematic. Not connected internally to any circuitry.
The reason for connecting this pin to GND is to achieve good RF grounding effect through that pin. In this way a good RF ground reference can be ensured for the VDD filtering capacitors by connecting the chip exposed pad's ground to the filtering capacitors' ground pads.