Vbat Current

dave23 · ‎2014-11-07

Posted on November 07, 2014 at 17:52

I am working with a STM32F051xx for a real time clock application. Looking at the datasheet (page 53, table28: typical and maximum current consumption from the Vbat supply), it is noted below the table that the MCU is placed under these conditions: VDD = VDDA = 3.3V

My question is: do the values noted in the Vbat supply consumtion table represent the consumption when the MCU is powered on? What if the MCU is powered off? Or inversely, if these values represent the current consumption of the MCU when it's powered off, what is the current consumption of the Vbat pin when MCU is powered on?

I'd like some clarification about this plz

Thanks

Chris1 · ‎2014-11-10

Posted on November 10, 2014 at 17:24

I don't know the specifics for F051, but generally speaking, STM32s have an internal power switch such that VDD is used to power the backup domain when power is present there, power from VBAT is used otherwise.

I doubt that the current draw, if any, from VBAT when there is power available at VDD is stated in a datasheet.

dave23 · ‎2014-12-02

Posted on December 02, 2014 at 20:37

The power switching scheme you describe is by far the most logical way to go, but my experience with another *cough* microchips *cough* manufacturer taught me not to trust the ''obvious logical way to go''...

Now that I'm migrating to STM32 MCUs, I pay some more attention to this kind of detail to avoid unpleasant surprises.

BTW, sorry for the late reply I was out of the office last two weeks...

Thanks for the info