How to power a STM32F746G-DISCO board from the CN6 VIN pin ?

[NMath.8]

Hi,

I'm trying to power a STM32F746G-DISCO board from the CN6 VIN pin.

I have a voltage regulator that output 11VDC current.

The screen turns on but the program never start and LD6 and LD3 become red after a few seconds.

I measured the current between GND and VIN, it's 11VDC , during few seconds, the it go down to 3.3V.

I measured the VO from the voltage regulator without connecting it to the board, and it's 11VDC stable.

The jumper is on V5ext, as explained in the documentation.

What is wrong with that setup ?

Everything works fine with USB.

[LMI2]

Voltage from your power drops to 3.3V? That can mean that either your power is not able give enough current or you have short or wrong connection somewhere.

[Tesla DeLorean]

How is the 24V DC grounded? Everything here share a common ground?

Tried connecting VIN, GND of DISCO via a bench supply? What kind of current is that pulling? Does that maintain 11 VDC on the VIN pin?

Anything else plugged into the shield connector? What's that doing?

[LMI2]

Have calculated have much your design dissipates power? This may be an overheat problem too. (40V-11V)/0.5A is not a little amount of heat. Use 5V switcher, it works, they come in to220 package.

[NMath.8]

Hi everyone,

Thanks for you answers and sorry for late reply. Didn't receive notification.

@Community member​ Everything share the same ground, which is the 24VDC power supply ground. So I connected the DISCO GND to the same ground. I didn't try to power the DISCO VIN directly to a bench supply. I will try it (will need to buy a bench supply :)) The shield contains other things, mainly external connectors (buttons, relay, RX/TX interfaces...)

@LMI2​ I use a 24VDC/3A power supply but the voltage regulator should output only 500mA. I will try with 5V switcher. Does something like that will work ? http://www.ti.com/lit/ds/symlink/lm2594.pdf . Thanks.

[NMath.8]

This is not clear for me how much current should I sent to the CN6 VIN pin. It's not written in the documentation.

I saw that the 5V pin have to be powered with a maximum of 500mA. But what about the VIN pin ? Is it also 500mA ? Is it better to power it more or less ? My LM317M output is exactly 500mA.

[NMath.8]

I tried powering the board directly with 5V through the JP2 connector, and I have the same kind of problem.

LD3 and LD6 don't blink but the screen turn on and off every seconds.

To power the board through JP2 connector, I used this breadboard : https://hobbyking.com/media/file/403178644X1017066X57.pdf

What is the best way to power a DISCO board without using the USB port ? Does anyone have a schematic that work ? If possible using a 24VDC power, but even with an other. Because I tried schematic with 12VDC, 24VDC... I'm not able to have something stable.

[Tesla DeLorean]

Current drawn is going to depend on the load presenting, for the bench supply case I'd probably set a max limit, but the purpose here is two fold. One to establish what the draw is, and the other that the platform is stable​.

I would start with 5V and establish a baseline.

Make sure the board has current ST-LINK firmware as V25 liked to clamp in reset with external power.​

[LMI2]

Yes, lm2594 would probably work but I would use these: https://www.digikey.fi/product-detail/en/recom-power/R-78E5.0-0.5/945-1648-5-ND/2834904. They are not IKEA style. Digikey has several similar models also for diffident voltages. Like Clive said, you really should check currents and power loss. The regulator I gave has 0.5A limit.

[T J]

You can't use the linear reg... and you need capacity.

" 317 is outputting 500mA," it must be burning.... 24V - 12 = 12V... @0.5A = 6 Watts

@LMI2​ has shown you the DC-DC converters, they work very well.

Its advised to use inductors in series to dissipate the switching noise, refer to the datasheet.

then your board will run a bit warm.... not blazing.....

then add minimum 1000uF before the reg and something 10-100uF after.

Low ESR caps are preferred, but not always necessary.

" 317 is outputting 500mA,"

Did you damage your board already ? looks like it.. :(

are any chips blazing too ?