BOOT0 votage level

[iHamd.1]

Hi,
I am using STM32WB55 device in my design and have to provide 3.3V from outside to BOOT0 pin BEFORE MCU is powered ON. In the datasheets and the manuals that I have been reviewing I didn't find any straightforward information what voltage level can be provided to this pin before device is powered-up.
Please let me know if someone have encountered with this topic before.
Thanks!

[AScha.3]

Hi,

>what voltage level can be provided to this pin before device is powered-up

Nothing ! Just pullup or connect to VDD of cpu, so pin is high when cpu gets voltage - thats it.

Only the boot0 pin...just use 10k pullup to 3v3, to limit the current to protection diodes of pin, as this is not any "normal" use of a pin, with unpowered cpu. See ds for safe limits on unpowered cpu.

[Andrew Neil]

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@iHamd.1 wrote:

 have to provide 3.3V from outside to BOOT0 pin BEFORE MCU is powered ON. 

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Really? What makes you think that?

As @AScha.3 said, you should not be applying power to any microcontroller input when the microcontroller is not powered - you can get some really weird effects doing that ... !

[iHamd.1]

Thanks for your replies!
What I see that it differs between devices: On this particular device the BOOT0 pin type is defined as "FT"
However, on TM32F411  (for example) the pin is defined as Input and permits up to 9V on it !!
Connecting BOOT0 to 3.3V wasn't of course the default choice, but application related scenario that can happen.
My idea was in that case to connect the pin to 3.3V not directly, but via 2K resistor in series that will in worst case force ~1.6mA into the pin. How harmfull you think it can be to the MCU?

[AScha.3 · Accepted solution]

I already wrote: > boot0 pin...just use 10k pullup to 3v3, to limit the current to protection diodes of pin

So, yes you could also use 2k , see ds for limits (injected current on this pin ).

+

9V at a pin will kill a STM32 cpu - except on this pin on F411 as info in ds. But better not try it...its still a 3v3 cpu.