Why is the rated supply voltage for the 5V pin regulator on the bluepill datasheet 4.0v and not 5v?

[HAbay.1]

I would like to know whether the stm32f103c8t6(Blue pill) can be supplied using a 5v source through the regulator ( 5V pin); I've seen a lot of people indicate that it was possible but the datasheet clearly says that the maximum voltage the regulator can take is 4.0v. In addition, I've read that the regulator is disabled in stop mode, does that mean that I cannot use my external 5v source in while in stop mode? and is the onboard usb regulator the same one used on the 5v pin? ( I've only seen one regulator in the blue pill schematic)

Image to see what portion of the datasheet I'm referring to :

[TDK]

You're confusing the onboard regulator which converts 5V to 3.3V with the absolute maximum input voltage of the MCU.

There is no problem powering the board from 5V USB under any operating condition because it it stepped down to 3.3V prior to going to the chip.

(There is also a regulator internal to the MCU which converts 3.3V to the working core voltage (around 1.2V) which you shouldn't need to worry about.)

[HAbay.1]

Got it , so the regulator stepping down 5v from the USB to 3.3v is the same one attached to the "5v" pin right?

[Tesla DeLorean · Accepted solution]

Providing the node names are case insensitive, the USB 5V and the board edge 5V go into the supply side of a 3.3V regulator that supplies the STM32. Lacking diodes I wouldn't push 5V in concurrently from the USB and board edge. You could also confirm voltages at key circuit nodes with a multi-meter or a scope.

https://freeelectron.ro/bare-metal-stm32-led-blink/blue-pill-schematic/

https://freeelectron.ro/wp-content/uploads/2019/12/blue-pill-schematic.png

[TDK]

Yes.
https://stm32-base.org/assets/pdf/boards/original-schematic-STM32F103C8T6-Blue_Pill.pdf