STM32L412 Standby+RTC battery current use

[mwp]

Hi all,

The STM32L412xx and RM0394 are quite clear about current use of the micro when in standby mode with LSI-RTC.

One thing the docs are not so clear about is the effect of having combined VBATT and VDD pins on the low pin-count packages. With these packages is the stated low (~700nA) standby current draw still possible?

So far ive been unable to drop the current draw under 5uA. This is my first foray into using the low power modes, is there anything else i should be looking for?

Thanks in advance.

[Sarra.S]

Hello @mwp, 

Could you please explain more your use case scenario/ hardware modifications?

[TDK]

Having combined VBAT+VDD shouldn't affect standby mode current consumption.

I don't see anywhere in the datasheet where it says 60 nA is possible with RTC/LSI in standby. I see more like 600 nA. Still less than the 5 mA you are seeing.

More details on the hardware would be helpful, including precisely where you are measuring current.

[mwp]

You are correct, i was remembering the standby value without RTC+LSI.
(ive updated the original post)

The test hardware at the moment is the L412KB Nucleo, testing current draw supplying VDD at JP1.

The Nucleo debugger via swd/swc is attached (im not sure if this make a difference during standby?).

[mwp]

As ive just replied below...

The test hardware at the moment is the L412KB Nucleo, testing current draw supplying VDD at JP1.
The Nucleo debugger via swd/swc is attached (im not sure if this make a difference during standby?).

The test is very similar to the example code in the "STM32Cube_FW_L4_V1.18.0/Projects/NUCLEO-L412RB-P/Examples_LL/RTC/RTC_ExitStandbyWithWakeUpTimer".

[waclawek.jan]

> The Nucleo debugger via swd/swc is attached (im not sure if this make a difference during standby?).

Yes, the processor may remain running due to debugging.

JW