STM32WL55 doesn't work with 1.8V

SMav · ‎2024-11-26

Hi,

I am working on a LoRa application with the STM32WL5MOC module which features the STM32WL55JC microcontroller. According to the datasheet, this module is compatible with a voltage level as low as 1.8V.

I am using the STM32CubeWL MCU Package for the firmware, and I have configured the Low Power (LP) mode for a 14dBm transmission power. However, the board stops functioning whenever the voltage drops below 2.05V.

Has anyone encountered a similar issue or have any suggestions on how to address this?

Thanks in advance!

Andrew Neil · ‎2024-11-26

@SMav wrote:
the board stops functioning whenever the voltage drops below 2.05V.!

What, exactly, do you mean by "stops functioning" ?

What board is this on?

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/ta-p/575228

PS:

Are you using VREFBUF:

STTwo-32 · ‎2024-11-26

Hello @SMav and welcome to the ST Community.

Could you please give more details about this behavior, your configuration, your design... it should be really helpful for our users to help you.

Best Regards.

STTwo-32

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SMav · ‎2024-11-27

Hi,

Thanks for the replies.

It is STM32WL STMod+ expansion board https://www.st.com/resource/en/schematic_pack/mb1779-high-band-b02-schematic.pdf

@Andrew Neil VREFBUF is disabled. RF stops transmitting when the supply voltage level is below 2.05V and I need to work with 1.8V for my application.

The hardware changes are as below:

Component	Modification	Description / comment
C1, C8, C14, C17	Fitted 4.7uF	bulk decoupling
C2, C12, C15, C16	Fitted 100nF	decoupling
CN5	2 pin header fitted	Used to power the board
JP2	fitted	to pass through power to module
U1	removed	RF switch
U2	removed	accel / gyro
U4	removed	barometer
U5	removed	RF switch
U6	removed	LDO 3v3
U7	removed	magnetometer
U8	removed	eeprom
U10	removed	serial flash
R12	shorted	set LP mode
R15	shorted	set LP mode
SB35	shorted	allow external supply
SB14	removed	disconnect onboard 3V3

Does anyone have any suggestions?

Thanks in advance!

SMav · ‎2024-12-04

Hey all,

Does anyone know a solution? Am I missing a step? Any help or suggestions would be greatly appreciated.

Andrew Neil · ‎2024-12-04

@SMav wrote:
It is STM32WL STMod+ expansion board https://www.st.com/resource/en/schematic_pack/mb1779-high-band-b02-schematic.pdf

Maybe it's a limitation of that board - rather than the chip itself?

SMav · ‎2024-12-04

All hardware from the board that could affect the module's behaviour at lower voltages has been removed, so the module is essentially isolated. This means it is the module itself and not other hardware on the board. The changes to the hardware are mentioned above.