STM32F042 blown up - what could be the reason?

andyandy91 · ‎2016-04-12

Posted on April 12, 2016 at 11:39

Hi there, we are prototyping a product that involves an STM32F042. It was working great but ... two units got the STM32 blown up! It just gets really hot and nearly pulls the VDD down.

Some details and ideas:

- We didnt accomplish the power ferrite / caps requirements, so only 2 caps were in the design, and no ferrite between VDD and VDDA was present. Now we've changed this, but could this cause the issue?

-There is a 3V3 CAN transceiver in the design too. Can this guy fry the STM32 for some reason? Overvoltage on the can lines? Voltage when VDDA was not ready on the STM32...?

-There is a USB device attached to the system. Only USB ground goes into. Could some overvoltage come from here and fry this? However, the DC/DC stage didnt suffer any damage...

-BOOT pin was pulled down to GND without pull-down resistor (changed now). Could this cause the problem?

Also, the units were hand soldered. This is for sure a source of issues, maybe there was some pin dodgy on the design ....

We have made all these changes on the design, however, any help/suggestion here is more than welcome.

Thanks so much.

#stm32 #can-bus #blown-up

Tesla DeLorean · ‎2016-04-12

Posted on April 12, 2016 at 18:21

I'm going to assume you don't have any sort of ESD protection on your external inputs. And that you haven't Xrayed the board to check for solder shorts, etc.

Think of silicon like a fuse, it is going to evaporate before a metal fuse will melt. It is quite easy to do a lot of damage, very quickly.

If it is a general failure, rather than limited to specific pins, I'd look at the power supplies, and their ability to handle large transients, and in auto-motive cases, load-dump.

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andyandy91 · ‎2016-04-30

Posted on April 30, 2016 at 13:53

Hi, no no ESD protection at all. We are also using a capsensing input, which means a large capacitor-plate in contact with a surface (could come from here?) - however this guy has a serial 1k resistor in order to keep ESD away (maybe not enough?).

We got a third unit blown-up. This time the STM32 just got really hot - but no VDD pulled down.

We are starting a new design, with some additional protections, and skipping the hand-soldering for sure.

Any suggestion? Although this above might fix the problem, I'd love to know the actual cause of it.

Cheers,

David.

Tesla DeLorean · ‎2016-04-30

Posted on April 30, 2016 at 20:08

I have very little insight into your design or why it would be failing. Something would seem to be very wrong to be destroying multiple devices.

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JulienD · ‎2016-05-01

Posted on May 01, 2016 at 23:46

Hi You should have a look to application notes for hardware design. They are really

usefull guides.

AN4080 is for your microcontroler.

http://www2.st.com/content/ccc/resource/technical/document/application_note/c9/19/d7/b8/6b/0e/4c/d3/DM00051986.pdf/files/DM00051986.pdf/jcr:content/translations/en.DM00051986.pdf

Julien

andyandy91 · ‎2016-05-04

Posted on May 04, 2016 at 20:00

Thanks.

Checked the AN4080 - I realized that all inputs are by default configured as inputs without pullup/down, which means that's the state of all my unused signals now (I didnt put any pull-up/down resistors on them).

I guess it's a good idea, turning the pull-up/down with the GPIOx_PUPDR registers?

Any risk to brick the micro if I do on swdio? I guess not, cause after reset it will hace its default state....

Thanks!