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stm32f429

kostas
Associate II
Posted on February 12, 2014 at 07:20

i've got a little problem with my board

a pin is shorted to the ground, only this input is shorted to the ground.

also shorting Idd pins, is shorting the supply power supply circuit and ldo going crazy hot

im thinking  replacing mcu chip, but im not sure if anything else is damaged

ldo still at 3V 

#discovery #stm32f429 #stm32f4
8 REPLIES 8
frankmeyer9
Associate II
Posted on February 12, 2014 at 09:11

I don't have a F429 discovery board (I view it as a rush job and ill-conceived design), but it most probably has the same Idd jumper as all other discovery board. These jumper is for current measurement, and not intended to short to ground under any circumstances. Either close it, or connect an ampere meter instead.

... shorting the supply power supply circuit and ldo going crazy hot ...

 

The power supply IC is surely going into thermal/current limitation mode. However, he would not survive such treatment indefinitely.

The good news - if you really short the supply, the MCU is not affected at all.

kostas
Associate II
Posted on February 12, 2014 at 23:56

shorting Idd makes board to stop working completly, and my computer running win7  reporting a usb power surge when im doing this.

all this hapened after tryed to measure with the internal A/D

an AC 4Vp-p signal on a DC offset at 18Volts

thought that adding caps to the pins and then applying the signal wont make any problems but sadly it did. the board turned off instantly, since then doesnt work.

the programmer looks like ok because computer recognize it as an ST Link dongle

thats why im thinking the mcu is fried

but even if mcu is dead it doesnt even worth replacing it with a new one because it costs almost the same as the whole discovery board

frankmeyer9
Associate II
Posted on February 13, 2014 at 09:11

shorting Idd makes board to stop working completly, and my computer running win7  reporting a usb power surge when im doing this.

 

Not sure if you speak about the present or the past.

But when shorting the 3V3 supply to ground, the MCU will certainly stop working, because it is not supplied any more.

all this hapened after tryed to measure with the internal A/D 

 

an AC 4Vp-p signal on a DC offset at 18Volts

 

thought that adding caps to the pins and then applying the signal wont make any problems but sadly it did. the board turned off instantly, since then doesnt work.

 

That sounds a little bit different.

18V are way above the 3.6V or 5V the datasheet specifies, so expect the MCU at least partially fried (protective diodes at GPIOs zapped).

but even if mcu is dead it doesnt even worth replacing it with a new one because it costs almost the same as the whole discovery board

 

I can't look at the board across this forum, but my first guess is it is dead - at least the target part. You may consult a hardware expert near you, to have a look at. But I would try to remove the ldo or the protective shottky diode (assuming the supply part is similiar to other STM32 discovery board I have), and check if the ''USB surge'' persists. Perhaps just some external and easily replaced circuitry (like the ldo) is fried up.

However, I would pal up with the idea to scrap the board, and file the issue under 'lessons learned'. BTW, I have killed much more expensive boards in my career ...

chen
Associate II
Posted on February 13, 2014 at 10:30

Hi

''all this hapened after tryed to measure with the internal A/D

an AC 4Vp-p signal on a DC offset at 18Volts''

18Volts !!

You have definitely killed the STM32. The datasheet specifically says that max voltage on the pins is limited to the same as the supply voltage.

Even trying to measure the 4V AC p-p is risky!

In future consider protecting the ADC with :

Shotky diodes

buffer OpAmp

Voltage Divider

kostas
Associate II
Posted on February 13, 2014 at 18:32

i measured resistance through the pin i applied this signal and its shorted to the ground,

only for this pin. rest pins are fine.

well yes after i understood my mistake now i've learned,

actualy i forgot that the inputs must have very high resistance shit happens

anyway learning through mistakes looks like its going to be expensive way

well if there were any protection diode to each input would be good things in case like this

if there is any protection diode to the board i guess it protecting from usb power supply not from input pins, or am i wrong?

chen
Associate II
Posted on February 13, 2014 at 19:36

''if there is any protection diode to the board i guess it protecting from usb power supply not from input pins, or am i wrong?''

Yes, the USB has protection. not sure what it is, sometimes it is a special chip which will isolate it when no USB is attached.

''well if there were any protection diode to each input would be good things in case like this''

All the IO pins will have some protection diodes for Electro Static Discharge.

None of them will protect the device from abuse such as over volting a IO pin.

It is up to the designer of the system to put in place adequate protection for all the off board inputs and outputs.

It is NOT up to the device vendor (STM) to provide protection to their devices from abuse (they cannot possibly know what people are likely to do with them. They have covered themselves by stating in the datasheet all the relevant absolute maximum/minimum values).

raptorhal2
Lead
Posted on February 14, 2014 at 22:12

actualy i forgot that the inputs must have very high resistance

Not true. ADC inputs should have low resistance so that the channel sample & hold capacitor can charge up to the input voltage within the sampling time chosen. The data sheet normal operating conditions ADC section provides the relevant data.

Cheers, Hal

kostas
Associate II
Posted on February 21, 2014 at 21:35

Thanks for the informations!!