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Questions About Using VDD12 on STM32L412RBT6P for Lowest Power Consumption

I'm working on a project using the STM32L412RBT6P microcontroller, and I have a few questions regarding the use of the VDD12 pins to achieve the lowest possible power consumption.
1. Can I directly connect the two VDD12 pins to a 1.25V supply?
2. What is the best exact voltage value to provide to these VDD12 pins for optimal power consumption?
3. After connecting the voltage to VDD12, are there any additional configurations or settings needed in the code to ensure proper operation and lowest power consumption?
4. I noticed in the  NUCLEO64 ext-SMPS (MB1319) documentation that there are four pins connected to the MCU GPIO: SMPS_SW, SMPS_PG, SMPS_V1, and SMPS_EN. Is it possible to only connect the 1.25V supply to the VDD12 pins and omit these connections?
5. I found an ultra-low power converter, the TPS62841, with an output of 1.25V. Would this be a suitable choice for supplying VDD12 to achieve minimal power consumption?
Any guidance or recommendations would be greatly appreciated.
Thank you!
ST Employee

Dear @Zaim01 ,


indeed that part number is designed to be used with external SMPS topology to reduce further the power and thus bypassing our internal LDO. 

The part number MCU having P or PTR suffix in the marking, i.e. STM32L412RBT6P) and it is connected directly to Vcore power line (Core, Memories and Digital peripherals supply).

Vdd12 power supply line can be used to bypass the internal LDO regulator when using an external SMPS.
In such a case you need to apply there voltage in range 1 .. 1.32V.
It doesn't require any external decoupling capacitor and it does not support any external load.

In case you would like to use an internal LDO, please keep this line unconnected.

More information on that you can find within dedicated application note, AN4978 "Design recommendations for STM32L4xxxx with external SMPS, for ultra-low-power applications with high performance"

Hope it helps you .