What voltage should be clamped on for analog input, vref or VDDA? At what condition positive injected current happen when the pin is used as analog input?
Hi,
I'm using STM32H7A3, and I’m a bit confused about injected current for pins used as analog input.
In our design, I used both 5V tolerant and 3V tolerant pins as analog input. And VDD=3.3V, VDDA is connected to VDD with a bead. And Vref is 3V. And for each input, I have clampon diode connected to VDD, not Vref.
For 5V tolerant pins, positive inject current would happen when Vin > min(Vdd, Vdda)+3.6V, with maximum 5 V.
For 3V tolerant pins, positive inject current would happen when Vin > Vdd+0.3V In the document here, chapter 5.2.1 and 5.2.2 https://www.st.com/resource/en/application_note/an4899-stm32-microcontroller-gpio-hardware-settings-and-lowpower-consumption-stmicroelectronics.pdf
If the pins are used as analog input, the maximum operating voltage on pin cannot exceed min(VDDA, VREF+) + 0.3 V. Does it mean injection current will happen when VIN > min(VDDA, VREF+) + 0.3 V, or the injection current will happen only when VIN > VDD?
The reason I ask is that I have clamp diode connected to VDD, not Vref. If injection current will happen when VIN > min(VDDA, VREF+) + 0.3 V, then the clampon diode can not really protect the design against accidently high voltage input.
Anybody can help me with this, any response is appreciated.
With best wishes
Jasmin
