STDES-WL5U4SBB: Clarification on FE_CTRL2 and FE_CTRL3 in HighBand HighPower

[rohithinthingstech]

I am developing a custom board based on the MB1720 HighBand HighPower reference design using the STM32WLE5CC microcontroller.

I need clarification on the operation and connection of the FE_CTRL2 and FE_CTRL3 signals that control the RF front-end switch (U3 - BGS12SN6):

What is the exact functional role of FE_CTRL2 and FE_CTRL3 in this configuration?

1. From the schematic, FE_CTRL2 is connected to PC13, and FE_CTRL3 to PA11, both controlling the BGS12SN6 SPDT RF switch.

2. How do these signals behave during transmit and receive? Which one is responsible for enabling TX and which one for RX?

3. Additionally, I’ve exposed these FE_CTRL lines to a connector (CN2). Is this standard practice, or should these only be internally controlled by the MCU?

[bmckenney]

[My experience is with the STM32WL55 (MB1389/MB1842), but this looks very similar.]

These pins are controlled by the software, as part of switching TX/RX. The functions can be found in the HAL BSP [stm32wlxx_nucleo_radio.c/.h]. You'll probably have to adapt RF_SW_CTRL_1_PIN et am. -- I suspect one of the three doesn't exist.

I'm not sure there's any point in bringing these out to pins; you might find use for Test Points.

[STTwo-32]

Hello @rohithinthingstech 

The RF states versus the switch configuration are given in the table below:

RF state	FE_CTRL1	FE_CTRL2	FE_CTRL3
IDLE	Low	Low	Low
High-power transmission	Low	High	High
Low-power transmission	High	High	High
Reception	High	Low	High

For the mapping of the FE_CTRL, it may be used but you can internally control them (without the connectors).

Best Regards.

STTwo-32