STM32f4 5V output pin

fiulala · ‎2015-07-20

Posted on July 20, 2015 at 12:42

Hi,

I'm connecting stm32f4-disco through USB to the computer and I'm measuring the 5v output pin from the board with a scope and I get 3,9 V. Did I burn it or something?

Thank you

megahercas6 · ‎2015-07-20

Posted on July 20, 2015 at 12:55

If you connect USB so VBUS pin of your STM32F4, it will generate high voltage on that pin group (DP+DM)

This is why you are getting high voltage, sometime that leaks to 3.3V rail, i learned this stuff the hard way. Check if PA9 is +5V, if yes and you want to run PA10 or PA12 at 3.3V, you must disable PA9 pin, usually that helps to disconnect 5V from other GPIOA pins or just cut the track

fiulala · ‎2015-07-20

Posted on July 20, 2015 at 13:45

I'm trying to do this:

And I get 3,9V not 5V

megahercas6 · ‎2015-07-20

Posted on July 20, 2015 at 17:23

Oh, output of USB is below 5V and is just 3.9V?

i figure GPIO output

3 possible scenarios:

1) Long usb cable, usually can give 4.6V even if small amount of current is used

2) i think this board has diode in series with usb, it is D2 BAT60JFILM diode, measure voltage drop on this part, anyway, it will be around 0.6V even at small load, so you will get only 4.4V on 5V pin

3) you have short circuit and it draws more than 500mA

fiulala · ‎2015-07-20

Posted on July 20, 2015 at 18:32

Thank you for reply.

The usb cable is short, like in the picture.

I think that the diode in serie with USB is D1. I get 5V on one side of the diode and 3,9V on the other side. I think this should be something like 5V and 4,7V.

megahercas6 · ‎2015-07-20

Posted on July 20, 2015 at 19:50

Just solder 0 ohm resistor. If you are not going to put any voltage to dev kit to 5V rail, it is not very useful. This is what i did, sine stm32f429i-disco with screen was getting low on voltage, after that it worked just fine :)