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AM4376: GPIO5_8 is pulled to +5V through 10K resistor, but it's power supply is 3.3V (VDDSHV3=3.3V). is there risk?

user3915702
Prodigy 80 points
Part Number: AM4376

Following is our schematic, since the power supply for GPIO5_8 is 3.3V (VDDSHV3=3.3V). So, we guess it may be a risk. how's the risk level?

Our product will released soon, we want keep the design and evaluate the risk.

  • 0
    TI__Guru 68880 points

    Yes, you are violating the absolute maximum voltage rating of the IO, which will eventually stress the IO to the point of failure.  I would say the risk is high, but the time to failure will differ from device to device.

    The schematic did not paste correctly.  Is there any way you can remove to pullup and still function properly?  I think this would be your only option with the current design.

    Regards,

    James

  • 0 in reply to JJD
    Prodigy 170 points

    Hi James,

    I want to have more discussion with you about this pull up voltage, I pasted the schematic again hope you can see it.

    From the schematic you will see the signal of AC_DETECT is pull up to 5V through a 10k resistor, and the MOSFET works as turn on/turn off of the AC-DETECT, we measured the voltage of AC_DETECT on our board during MOSFET OFF, it is about 3.568V, not exceed 3.6, from the datasheet of AM4376, it doesn't exceed the maximum voltage rating but very very close to it.

    Can you explain why the voltage is 3.568V, not 5V?

    And the current is very small 5V/10K less than 0.5mA, do you think this current level still have high risk of CPU IO? if yes, can you explain why this CPU I/O is so weak to have high risk of damaging with so lower level current, because in the real working environment, the ESD or other interference signals(like unstable electrical grid) can cause the IO signal exceed the 5V.

    Thanks and best regards

    Kelvin

  • 0 in reply to lesheng cao
    Prodigy 80 points

    Hi James,

      Could you please answer my colleague Kelvin's concern? Thank you!

  • 0 in reply to user3915702
    TI__Guru 68880 points

    the measured voltage is most likely derived from the voltage divider of the external pull up and an internal pull down on the GPIO.  You should not rely on any internal resistor for voltage divider.  It needs to be taken care of external to the device. 

    Ultimately, the voltage levels at the pin need to conform to the DC electrical characteristics and the Absolute Max Ratings specifications in the datasheet.  The IO voltage at any pin should never be higher than the IO supply voltage +0.3V.  If it is, you risk damage to the IO

    regards,

    James  

  • 0 in reply to JJD
    Prodigy 80 points

    Thank you! James!

    we clearly understand the issue now.