Dynamic switching between native TX power and nRF21540 FEM on nRF54L15

[Ziyao Zhou]

Hi Nordic team,

I noticed that when using the external FEM (nRF21540) with the nRF54L5 device, the power consumption at a transmit power setting of 8 dBm is significantly higher compared to using the native radio TX power at the same 8 dBm level.

In my application, I need to dynamically adjust the transmit power in the range of 0 dBm to 20 dBm. To optimize overall power consumption, my plan is to use the native radio TX power for levels below 8 dBm, and switch to the FEM for higher output power above 8 dBm. I intend to implement this using an RF switch architecture similar to the one used on the nRF7002 DK.

From my understanding, MPSL is a key component for controlling and driving the FEM timing. My question is: Is it possible to enable or disable MPSL dynamically during runtime while the application is running?

Any guidance or recommended design approach would be greatly appreciated.

[Simonr]

Hi

Hi

The FEM layer of the MPSL does a lot of this work for you, so you don't need to worry about a lot of this. Please go through the documentation here for details. https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/app_dev/device_guides/fem/index.html 

The MPSL is a build time setting, so this is not configurable during runtime as far as I know.  https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/app_dev/device_guides/fem/fem_mpsl_fem_only.html 

Best regards,

Simon

[Ziyao Zhou]

Thank you for your reply!

So that means there is no way to switch between MPSL on and MPSL off.

In my application, I need to dynamically adjust the transmit power in the range of 0 dBm to 20 dBm. To optimize overall power consumption, my plan is to use the native radio TX power for levels below 8 dBm, and switch to the FEM for higher output power above 8 dBm. I intend to implement this using an RF switch architecture similar to the one used on the nRF7002 DK. Is there any way to do such application?

[Simonr]

Hi

Yes, this should be possible, but you will need a physical RF switch, as there is no API for doing this. You will need to "fool" the MPSL to output 8dBm while it thinks the FEM is still connected I think, or you can use GPIO only mode.

Best regards,

Simon