Data Sheet

BMD-345 - Data sheet
UBX-19039908 - R07 RF front end – PA / LNA Page 19 of 36
Agency
World region
Maximum nRF52840
transmit power setting
RFX2411 mode
during transmit
Limitations
FCC
USA
−8 dBm (0x000000F8)
PA transmit
enabled
When using 802.15.4 (O-QPSK) – Channel 26 (2480MHz):
Max NRF52840 TX Power setting: +6dBm (0x00000006)
RFX2411 Mode during transmit: Bypass Mode
ISED
Canada
−8 dBm (0x000000F8)
PA transmit
enabled
When using 802.15.4 (O-QPSK) – Channel 26 (2480MHz):
Max NRF52840 TX Power setting: +6dBm (0x00000006)
RFX2411 Mode during transmit: Bypass Mode
CE-RED
Europe
−16 dBm (0x000000F0)
PA transmit
enabled
Table 15: Regulatory transmit power limits
⚠ u-blox recommends consulting with an accredited certification agency to obtain the transmit
power limit information for all world regions.
5.2 Software Enablement
There are two methods for implementing control of the PA / LNA: dynamic and static. Using the
dynamic method, full control of the PA / LNA is possible. Using the static method, only shutdown and
bypass modes are available.
5.2.1 Dynamic Method
The dynamic method for enabling PA / LNA provides full RF performance but requires precise timing
of the control signals. The PA must be turned on right before each transmission and then turned off
after; same for the LNA. Some software stacks such as the Nordic Semiconductor SoftDevices
support a PA / LNA with a simple configuration (SoftDevice S140 v6.1 / nRF5 SDK v15.2 or newer
required). Zephyr can be configured as well but requires a bug fix (as of Zephyr 1.13.0). Support can
be manually implemented as well, provided user code can be run between each transmit and receive
context switch.
The typical implementation uses the nRF52840’s Peripheral-Peripheral Interface (PPI) and GPIO Task
Event (GPIOTE) to automatically toggle the PA / LNA control pins, TX_EN and RX_EN. In the sequence
below, the highlighted events (EVENTS_READY and EVENTS_DISABLED) are used to trigger the GPIOTE
peripheral tasks (TASK_SET and TASK_CLEAR, respectively). This requires two PPI channels (1 and 2 are
used in the example), and one GPIOTE channel (0 is used in the example) that are reconfigured
between when the radio needs to transmit and receive. This method enables the GPIO to be toggled
automatically for every radio packet, however the GPIOTE needs to be reconfigured when switching
between modes in order to toggle the correct pin for the required mode.