Voltage withstand of MCU pins

[Lyu.1]

Hi,Master:

platform: STM32G070CB

phenomenon:
When the MCU is empty (without any program), connect an external pull-up resistor 10K to the adjustable voltage source on the PA4 pin, adjust the voltage in the range of 4~18V, and find that the maximum clamp of the PA4 pin is about 5V, and then test that the pin is not damaged

I suspect that this phenomenon was formed by the TVS tubes connected in parallel at the time.

My questions are:

Q1. Is there a TVS tube inside to the ground ？

Q2. What are the breakdown and recovery voltages for the TT_x and FT_x type pins?
Q3. The external voltage passes through the resistor to the pin, no matter how large the external voltage is, just make sure that the pin voltage is within the maximum range (the table below) when designing, right?

For example, if 20V passes through a 33K resistor to a FT_a type pin, this pin is configured to open the drain, and the test is tested as long as the voltage on the pin is < VDD + 4.0

Thank you very much!

[TDK]

1) All GPIOs have protection diodes. You should generally not rely on these to protect the chip.

2) Generally, just over VDD + 4 V. Exact values are not specified.

3) No, you're applying more than VDD + 4V to the pin, so that's outside of the absolute maximum value and you are now injecting current into the chip, about 0.6 mA. Look at the table for max injected current.

No positive injection current is allowed.

[Lyu.1]

Thank you for your guidance.

Regarding the above 3), External voltage passes through a 33k resistor to the pin, if VDD=3.3V, external voltage:
a). At 6V, 6<VDD+4, will there be no current injection at this time? So is external voltage safe for the system at this time?
b). At 10V, 10>VDD+4, the injected current is (10-3.3)/33=0.2mA. It's not safe. Is this understanding correct?

[TDK]

a. If it's an FT_xx pin other than an FT_c pin and pullup/pulldown is disaled, yes. Otherwise no. Note that PA4 is a TT_a pin and the absolute max voltage is 4 V.

b. Correct.

[Lyu.1 · Accepted solution]

You solved my doubts, Thank you very much!

[Lyu.1]

Master,I'm sorry, Please allow me to ask one more question:

The red line indicates that it may not be able to work properly for a long time at the maximum rating? If so, if it only exceeds a certain standard value and is less than the maximum rating for a long time, can it be guaranteed to work normally for a long time? For example: a) (discussed earlier) At 6V after 33K resistor to FT_xx pins except FT_c, it is greater than 5V but less than the maximum rated VDD+4, can the pins work properly for a long time in this scenario?

Thank you very much!

[TDK]

Conditions outside of the standard operating conditions but below absolute maximum ratings are in the gray area. The manufacturer does not make and guarantees here and you should not design a product that causes pins to be in this state. Things will generally work, but it is not guaranteed and not advised.

If you can mark my response as the answer, I'd appreciate it. That's usually how it goes.

[Lyu.1]

Ok, thank you very much for the suggestion.

[Techn]

It  is bit confusing.. In Microchip documentation, for many examples, they rely on the ESD protection diodes to  limit the voltage if the current is limited. Are there ESD protection diodes to Vdd and Vss or only towards VDD?

The above is from STM32Datasheet