STM32WL30 Reference Design

[Tobias3]

The Application circuits in the Datasheet under section 5 do not list any values for the components, are they available somewhere? All of the reference designs linked in the wiki and on the website are for the STM32WL33C. Do the values directly transfer over? We are also explicitly interested in the configuration without the SMPS as there are no application examples for the STM32WL33C without the SMPS and it is not clear which components can be removed when not using it.

[Saverio GRUTTA]

Hello Tobias,

Yes I confirm that also for the STM32WL30 you can refer to the following data brief:  Data brief - STDES-WL3xxxxx - Reference designs for STM32WL3x microcontrollers.

The reference design in this document is for the VFQFPN48 package. However, you can start by using the bill of materials (BOM) from the reference that is closest to your radio frequency configuration. Please share your target RF configuration, including the center frequency, output power, and the number of layers for the PCB you plan to design.

Regarding the question about the SMPS, in this case, the power amplifier (PA) is supplied by an external supply. Remove inductors L1 and L2, leave VLXSD floating, and connect VFBSD to VDD.

Note that using this configuration degrades the efficiency. Could you provide the operating range of VDD for the project?

Best regards

Saverio

[Tobias3]

Thank you for your quick response, this clears up a lot of confusion on our end.

We are planning a two layer board with 10dBm in the 868MHz band. Only the transmitter has a limited power supply. The receiver runs on mains and we deemed the BOM reduction worth it compared to the gain in power efficiency, especially because the receiver rarely transmits and almost always runs in RX mode which leads to the SMPS being bypassed for optimal sensitivity anyways. The MCU on the receiver runs at 3.3V.

[Saverio GRUTTA]

Hello Tobias,

We can refer to the reference design STDES-WL3C2SLH | Product - STMicroelectronics. If you limit the output power at 10 dBm you can connect the chock inductor of the PA directly to VDD. 

Best regards

Saverio

[Tobias3]

Thank you very much for you help.
I assume the choke inductor is L8? And directly to VDD means that C14 and C15 can be removed?

[Saverio GRUTTA · Accepted solution]

Hello Tobias,

I confirm that L8 is the choke inductor for VDD. I suggest including at least the footprint for one capacitor. Depending on the layout, this could allow filtering of the supply voltage to help avoid spurious emissions.

Best regards

Saverio