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WARNINGS on VOLTAGES and BOARD DESIGN

Question asked by jlc.jlsilicon on Jul 22, 2012
Latest reply on Jul 24, 2012 by Andrew Neil
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. 

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