WARNINGS on VOLTAGES and BOARD DESIGN

jlchoobs · ‎2012-07-22

Posted on July 22, 2012 at 12:21

I have been building my own Boards.

And have experience with an assortment of Micros.

WARNING #1 :

I have found that these STM Chips are Very SENSITIVE to Voltages.

I accidentally tied the USB 5V source to the VDD Bus thinking that it could also Power the Chip - accidentally for a few Seconds. Now the STM32 Chip and Board are USELESS.

Do NOT use ANY Voltage HIGHER than 3.5V on ANY Pin to the STM32 Micros -or the Chip becomes ABSOLUTELY USELESS. Flash Programs will Not Execute -and the Programmer will Not recognize the STM Chip anymore.

The other chips, atm for example, are not so Sensitive. And, I never encountered issues with brief stray Voltage Levels.

All I can say is Be Careful as can be.

And if you think that the STM is Not responding to the Programmer - then it is probably so - and a waste of time to try to resurrect the Chip.

What threw me off is that the Stm32 Micros can Not be Directly powered off of the USB Bus (as I would at first assume). You need to place a VReg (like 3.3V) between them.

jlchoobs · ‎2012-07-22

Posted on July 22, 2012 at 13:08

WARNING #2 :

Do Not FORGET to connect VCAPS = 2.2uF on the STM32f4nn Chips also.

Do NOT tie them to GND like the Stm32f103 Micros - or again you will BURN OUT the Chips and they become USELESS.

Do-No-Pass-Go -- Do-No-Collect-200-Dollars

The Manuals are NOT Explicit enough - STM states that the Stm32f405-7 chips are PIN COMPATIBLE with the Stm32f103 Micros - which is NOT CORRECT.

Two of the GNDs on the Micros are now VCAP Pins which need to be tied to 2.2uF Caps which then connect to GND.

I have Two USELESS CHIPS and BOARDS - One was caused by THIS Same MISTAKE.

Take Note of This Design ISSUE !

jlchoobs · ‎2012-07-22

Posted on July 22, 2012 at 13:21

WARNING #3 :

If designing or wiring the Micros yourself.

Place a 220 ohm or higher (up to 1K) Resistor betwen the MmcCard Pins and the Stm32 Pins. Do the same with any other Input Pins frm other Devices or Chips.

This is in case that (your) Program changes the Direction of these Pins - so you dont BURN OUT your IO Pins. I have done this in the past.

Oops ! - I accidentally Output to PortA pins (which is MmcCard) - instead of PortB Pins where my LEDs are.

So, there goes your Output Pins - and so the Chip becomes Useless for Your Project - unless you want to switch the MmcCard Pins (not so easy).

jlchoobs · ‎2012-07-22

Posted on July 22, 2012 at 19:49

#4 : Then there is the USB tweak needed ..

I wish these micros actually worked when setup as stated in the Spec - and as smoothly as the Demo Boards.

I find that I need to scan over the Demo Schems again-and-again because of unexplained problems and needed solutions ...

stm32forum · ‎2012-07-22

Posted on July 22, 2012 at 21:05

I have found that these STM Chips are Very SENSITIVE to Voltages.

I accidentally tied the USB 5V source to the VDD Bus thinking that it could also Power the Chip - accidentally for a few Seconds. Now the STM32 Chip and Board are USELESS.

That has nothing to do with Very sensitive, 5V is away above the specs even if you do it for a few seconds.

It's just not paying enough attention that you fried the Stm32, don't blame Stm for it.

Andrew Neil · ‎2012-07-22

Posted on July 22, 2012 at 23:43

''That has nothing to do with Very sensitive, 5V is away above the specs''

Indeed it is!

The OP didn't say which particular ''STM32'' device(s) was/were affected, but here's a link to the STM32F101x8/STM32F101xB datasheet:

http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00161561.pdf

The Absolute Maximum specification for Vdd is 4.0 V

The USB ''5V'' could be up to 5.25 V - so this could be exceeding the Absolute Maximum specification by 30%!

''don't blame STM for it''

It's only doing what it says on the tin!

emalund · ‎2012-07-23

Posted on July 23, 2012 at 17:22

I wish these micros actually worked when setup as stated in the Spec - and as smoothly as the Demo Boards.

I find that I need to scan over the Demo Schems again-and-again because of unexplained problems and needed solutions ...

does te fact that the demo board work ''smoothly'' not tell you something?

if you followed the specifications and adhered to good layout practices, there would be no ''unexplained problems''.

that a 3V3 chip blows when 5V is applied is not that the chip is ''very sensitive'' try it with virtually any chip and the result will be the same.

Erik

jlchoobs · ‎2012-07-24

Posted on July 24, 2012 at 19:41

I am talking about the USB not working while following Spec.

I still do not have the USB working on my own Boards (while it does work on the Demo Board). And, I followed the Demo Brd Schem explicitly.

Except that I did not add the EMID02USB03F2 chip. Is this neccessary ? - It was not suggested in the Specs.

jlchoobs · ‎2012-07-24

Posted on July 24, 2012 at 19:47

As for the loose criticism here.

Note that it is explained to connect the VBUS=+5V to PA9 pin - which is what made me think to also connect it to Vdd. This is what threw me off.

I don't know too many logic chips that the IO pin input voltages can be greatter than the chip's Vdd.

Which breaks your same rule from Spec.

By the way has anybody etched their own boards for Stm Chips ?

- Who can offer any useful advice ...

jlchoobs · ‎2012-07-24

Posted on July 24, 2012 at 20:01

Great Ren and Stimpy - glad you can COUNT and ADD ...

I think any one reading these Forums doesn't need such Obvious notes though.

I already stated that.

But in you mentioning it, you are forcing me to explain that the atml chip are Not Sensitive as these chips are. I have used them for years without blowing any chips. Also the chips were more flexible with components - and I had built many boards without problems that I am having here. Usb and Mmc and Analog devices worked fine with minimal effort. I also could run them off of a couple of AA Batteries without needing a VReg or VMult - not like here.

Thanks for making my point for me guys.

You have your uses for me. 🙂