Powering up stm32

[Nidhal Abidi]

Posted on April 17, 2018 at 17:43

which is best to power up    ''' STM32VLDISCOVERY '''   via 5V pins and a ground or 3,3V ???

also which is best to for Digital Input for STM32VLDISCOVERY, using 5v or 3,3V ???

In the data sheet I found that bouth of them works. And when I tryed it, bouth works but in the data sheet reset button and pin PA0(user button) are related to 3,3V.

so wich is the best chice for an industrial

project ???

[Andrew Neil]

Posted on April 17, 2018 at 19:07

What do you mean, 'best' ?

As you can clearly see from the schematics, the STM32 itself is running from 3V - so the only difference between powering the board from 3V or 5V is whether or not it goes through the regulator first.

Check the datasheet for details of the '5V tolerant' pins.

Also check the datasheet for details of the logic thresholds, but I think you'll find this is set by the STM32's supply voltage (3V) - so you gain no advantage from 5V logic levels.

undestrial

You mean, 'industrial' ?

Note that the Discovery boards are supplied by ST as an evaluation tool - they are not intended as final products, and the licence terms specifically prohibit such use.

[Nidhal Abidi]

Posted on April 18, 2018 at 11:57

Thanks, mmm, what if I power up the stm with 5v and then use the stm's 3.3v out as inputs for the switches, or buttons or whatever ???

[Andrew Neil]

Posted on April 18, 2018 at 12:21

Nidhal Abidi wrote:

 what if I power up the stm with 5v

Have you actually looked at the datasheet for the STM32 chip?

It tells you what range of voltages can be used to 'power-up' the chip ...

[AvaTar]

Posted on April 18, 2018 at 12:28

Have you actually looked at the datasheet for the STM32 chip?

And the schematics of your Discovery board, too ?

It would tell you that the 5V input path feeds the 3.3V path that supplies the MCU.

The 3.3V supply path bypasses the regulator, and supplies the MCU directly.

BTW, I would really upgrade to another board (e.g. a Nucleo).

The ST-Link V1 on the VL-Discovery is a mess, nothing ST could be proud of.

[Nidhal Abidi]

Posted on April 19, 2018 at 09:37

Great thanks.

[Nidhal Abidi]

Posted on April 19, 2018 at 09:22

Yeah actually I don't wanna work with it. I did read the datasheet.  as you know the regulator could be so hot, that's why I'm not sure about making it work for a long time with 5V. I just wanna be sure.

[Andrew Neil]

Posted on April 19, 2018 at 09:34

Nidhal Abidi wrote:

I don't wanna work with it.

Don't wanna work with what ?

I did read the datasheet. 

So you know the acceptable range of supply voltages.

as you know the regulator could be so hot

Only if you have not correctly designed it - including providing adequate provision for heat dissipation 

I'm not sure about make it work for a long time with 5V.

That's just basic electronics - nothing specifically to do with STM32

[AvaTar]

Posted on April 19, 2018 at 09:40

... as you know the regulator could be so hot, that's why I'm not sure about making it work for a long time with 5V.

It should not.

The 5V-to-3.3V regulator is a linear type, that dissipates

((Vin - 3.3V) * Iout)

as heat. So either your input voltage is higher than necessary, or something draws too much current. Or both.

I had worked with the VLDiscover, and they never got hot.