In which cases should I apply DC-DC to PAVDD when creating an EFR32 Series 1 design?
Using the 1.8V output of the internal DC-DC converter of EFR32 Series 1 devices for DC supply of the PA provides better efficiency (i.e. lower PA current for the same output power) compared to the case when the PA is running from the main 3.3V. The recommendation for applying the DC-DC output to PAVDD:
Above these power levels, using the main 3.3V supply for DC supply of the PA results better efficiency.