5V FT pins vs. injection current on STM32G0

[Carl_G]

I am confused about the limits of the FT pins on this MCU. I think I understand the maximum voltage on an FT pin except FT_c is Vdd + 4V as long as no pulls are enabled. So with 3.3V Vdd the max voltage on most FT pins will be 8.3V is that correct? Its a bit confusing where that footnote is placed.

Beyond that, given the voltage limit is 8.3V how does it matter if the positive injection current limit is 0mA? That means I need an infinitely large resistor to prevent any injection current when the voltage is over Vdd. Or does N/A mean there is no current limit so long as the voltage is not exceeded?

Thank you.

[TDK · Accepted solution]

> Or does N/A mean there is no current limit so long as the voltage is not exceeded?

Yes, basically this, but a few things to note here:

• Positive injection is not possible on those pins if they are below the voltage threshold. So you need to respect the voltage threshold, and the current injection is satisfied automatically.
  • 
• The "Absolute Maximum Ratings" should not be encountered during normal operation. Per the datasheet: "Exposure to maximum rating conditions for extended periods may affect device reliability."
• The max allowable voltage during normal operation is min(VDD + 3.6V, 5.5 V) for FT pins.
  • 
• (also minor note: 3.3 V + 4 V = 7.3 V, not 8.3 V)

*STM32 microcontroller GPIO hardware settings and low-power consumption - Application note

[Carl_G]

@TDK When you say positive injection current is not possible, you mean because of the internal circuitry it won't allow positive injection current until the voltage is above the given value? As you point out, 7.3V in this case.

[TDK]

Correct.