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Will this signal destroy my uC pin?

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eTobey:
Hi,

my signal generator does some not so pleasent pikes when it is turned off.
I wonder if my inputs (3.3V) will take immediate damage, or if it takes a few of those pulses (10, 100, 600?).

Anyone has some references or knowledge?

ebastler:
It might help if you tell us what µC you are using...

Also, have you checked the output impedance of that transient voltage pulse? How does it look if you put e.g. a 1 kOhm resistor in parallel?

nctnico:
A better approach is to have protection on pins. Even if it is just a prototype board. It saves a lot of trouble and time.

tom66:
It may well do so.

Likely your signal generator has a 50 ohm output termination.  The damage threshold for the ESD diode in the pin may be around 10mA and the clamping voltage will be Vcc+0.6V typically.  So you can calculate that the current will be approximately (Vout-Vcc+0.6)/50 once over this threshold.   Solving for Vout assuming 10mA maximum and assuming Vcc of 3.3V gives you 4.4V as the absolute maximum voltage that can be output from the signal generator, before its internal termination, before damage occurs. 

Test the signal generator output voltage with no MCU connected on power off and see what voltage it goes to, to determine the maximum open circuit voltage.

Note that the pin might withstand higher currents for a brief period of time, but there is no guarantee of this and progressive damage can occur causing the IO structure to failure.  In many cases, this will cause a dead short from 3.3V to ground, but in some cases it can just damage that IO pin.

Also, note that ADC channels on many microcontrollers will misbehave if just one input is overstressed.  I have a PIC32MM board here where that was a problem, we had to change divider resistors to ensure no channel ever went above Vcc as it caused adjacent channels to misbehave. 

eTobey:

--- Quote from: ebastler on May 17, 2024, 03:50:45 pm ---It might help if you tell us what µC you are using...

Also, have you checked the output impedance of that transient voltage pulse? How does it look if you put e.g. a 1 kOhm resistor in parallel?

--- End quote ---

Its a STM32G431 RBT6.

With 1k, the max value goes down to 5V.


--- Quote from: nctnico on May 17, 2024, 03:51:58 pm ---A better approach is to have protection on pins. Even if it is just a prototype board. It saves a lot of trouble and time.

--- End quote ---
Of course i have those on my prototype, but right now im testing with a nucleo board. I dont think it has any protection.

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