What pins to power STM32F411CE with

[KClos.1]

I'm making a PCB for a project and am using the STM32F411CE (Otherwise known as the "Black Pill"). However, after spending many hours looking through the data sheet and searching online I'm still not 100% sure I understand how to power this board via battery. From my understanding the board does not have VDD and VSS pins. The only pins that I can tell are able to be used for power are 5v and 3.3v pins.

As per the datasheet, the board should not be powered by more than roughly 4v. That leaves me with just the 3.3v pins. Any other board I have used in the past has had VDD and VSS pins so I apologize if this is a silly question.

So my question is this, is it as simple as connecting 3.3v from a battery to the 3.3v pins and ground?

I am also a bit confused about whether I can power the board with 5v. As I stated earlier, the datasheet says not to exceed roughly 4v. However in the image below that source states there is a regulator that supports up to 6.0v.

 

So can I power the board with 5v after all?

[Bouraoui Chemli]

Please refer to application note AN4488 "Getting started with STM32F4xxxx MCU hardware development". It provides an overview of the hardware implementation of the development board, with focus on power supply and other features.

[KClos.1]

The application note has useful information but doesn't answer all my questions. In the application note it still refers to the "VDD pin" which I'm still unsure of what pin that is.

I'm simply asking which pin I connect my battery to to power the board. 5v pin, 3.3v pin, or vBat pin?

[Peter BENSCH]

You are confusing a few things here: the AN4488 refers to designs that use an STM32F4 directly.

But you want to use the MiniSTM32F4x1 board from WeActTC aka BlackPill, which is actually designed to be powered via USB or the 5V connector.

If you do not use the 3.3V connection to supply smaller external loads, but to feed in the 3.3V, you could run into unforeseen problems. This is because you are operating the LDO AP7343D-33FS4-7B backwards, since the p-fet it contains usually has a parasitic antiparallel diode with an anode at the regulator output. This diode path conducts as soon as the output has a higher potential than the input - i.e. when 5V is open.

By the way, this LDO can handle voltages up to 5.25V.

To get back to your question, which would actually be better served by WeActTC or Adafruit or where you bought it:

• the Vbat connector is only used to buffer the Vbat domain of the STM32 (for RTC, buffer RAM), not to power the board; for more details see the datasheet of the STM32F411CE
• 3.3V is an output and very likely not suitable for feeding in
• 5V would be the perfect input, as the LDO has a drop-out voltage of max 0.29V at 300mA, so you can go down to 3.3V+0.29V=3.59V with the input voltage at this pin

Does it answer your question?

Regards

/Peter