5V Tolerant (FT) Input Pin with Internal Pull-down Resistor on STM32H753ZI

[aditya3]

Hi,

I am using a STM32H753Zl MCU and have configured an FT pin (PCO) for 5V digital inputs. However, since the pin is floating I have enabled the internal pull-down resister via CubelDE. While testing it worked fine, but is there any
damage this could cause to the board in the long run?

Thanks

[Peter BENSCH]

If you look at the data sheet, you will find two statements:

Section 7.2, table 118:

• VIN, Input voltage on FT_xxx pins = max Min(VDD, VDDA, VDD33USB, VBAT) +4.0V
• Footnote (4): To sustain a voltage higher than 4V the internal pull-up/pull-down resistors must be disabled.

This means that the pull-down can withstand 5V when VDD is applied - the emphasis here is on ‘applied’. If VDD is switched off and therefore 0V, you exceed the above condition by 1V.

Hope that helps?

Regards
/Peter

[aditya3]

Yes thank you. Just to confirm, that means that if VDD is applied then there is no issue with using an internal pull-down resistor and the pin can withstand 5V?

[Peter BENSCH]

Correct.