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I am currently making a project with the stm32f3discovery board and am ready to move it away from the computer and onto an external power source. I have a 5v ubec connected to a lipo battery and am getting about 5.2v from the ubec, when plugging it into the 5v pin it all turns on and runs fine but then after a few days the board started to not run and then got to the point where I can't even flash code to it anymore. Is this the fact that it's 5.2v and not 5v or is there something else going on here that i'm not aware about.

There doesn't seem to be anything online about how to power it from an external source except from in the user manual but it doesn't say how close to 5v it has to be.

From the user manual

Also what are the white circles for next to the 5v and 3v pins?

Any help will be much appreciated, thank you.

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  • \$\begingroup\$ Most like this is a "something else going on". What feeds your UBEC? Is this a drone? Keep in mind that board is a development and demonstration platform, it's not engineered to be used - it's big, has lots of extra parts, etc... One of those extra parts is the on-board ST-LINK, right now it's not clear if your issue is with the target F3, the F1 comprising the ST-LINK, communication between them, other parts on the board... \$\endgroup\$ Jul 1 '20 at 13:21
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The white dots tell you where pin 1 is on the connector. You can also see that the solder pad is rectangular and not circular - which indicates the same on copper level.

If you have a look at the schematic you see the board uses a LD3985M33R to generate the 3.3 V out of the 5 V. The datasheet of that part indicates that it is able to run up to 6 V. It will be able to generate the 3.3 V down to an input of 3.4 V.

So from that I'd say 5.2 V is not inherently the problem. Depending on what the UBEC (whatever it is) does it can still damage the board.

The discovery boards do not include protection devices of any sort - so a voltage spike beyond 6 V could damage the whole thing. As will static discharge of your cat or a lot of other things which can go wrong. These boards are nice to evaluate the chips and build small projects which are not required to be rock solid. If you made the experience, that the MCU is able to do what you need and you need it 24/7 it's time to move on and make your own robust design.

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  • \$\begingroup\$ I found out the issue was with a bit of coding. Adding PA11 and PA13 onto timer 4 whilst it was already set up to two pins on port D seemed to break the STM32, and wiping the board with the st-link application seemed to do the trick. Although thank you so much for taking the time anyway as I was still not sure about if wiring it up like that was actually the right thing to do as their doesn't seem to be much else out there. When i have finished the project completely I will look at making my own pcb but for now I am a few steps behind that. \$\endgroup\$
    – Jack F
    Jul 2 '20 at 17:11
  • \$\begingroup\$ @JackF interesting. I'll keep that in mind. You could also post this as an answer and mark it as correct (as it solved your problem) instead of mine. \$\endgroup\$
    – Arsenal
    Jul 3 '20 at 6:27

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