Can I use your FEM driver for BL5340PA to change gain value on the nrf21540?

We don't currently support changing the gain of the FEM to lower power with an API. This is not supported in the Nordic driver. The FEM has two calibrated gain settings - one that achieves 20 dBm output and one that achieves 10 dBm output (both with 0 dBm input). However, you can change the output power level as discussed in the following FAQ.

 Can I lower the TX Power on the BL5340 from the maximum set by the FW? (