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nRF52840 - Can I switch off protection diode inside of GPIO?

gmonroe

I have a problem on a first prototype where one of my ICs is putting out an out of spec 5V which goes into P0.26/AIN4.  It appears to be back driving the 3.3V rail in my processor possibly going through a protection diode.  I end up with around 3.8V which is then propagated out Vdd/Vddh and goes to the rest of the board.  The 1.2V drop appears to be a bit more than a single diode drop, so there may be a bit more going on here.

I understand that this is not good for the processor, but I am looking for a workaround for a demo while I solve this issue with my other IC.  Is there a way to tri-state everything including the protection diode on the GPIO to avoid the back driving voltage?  This may be normal operation, but I have not been able to find a good enough diagram of the GPIO yet in order to verify that.

Thanks.

  • 0

    Simple answer is no; maybe you could add a level shifter or a voltage divider or several series diodes in the line to the input pin. Note absolute max Vcc on nRF52840 is 3.6V so extended exposure to 3.8V via the backdrive/phantom power will eventually lead to damage of the nRF52840.

  • 0

    If you mean the ESD protection diodes, then no.  They cannot be. 

    Which is a issue if any voltage is present when power is turned off.  This is because voltage WILL leak thru the protection diodes and could (and probably will) power our device.  Also, that 5Vdc is out of spec and should have some sort of voltage leveler (shifter)  used to prevent this Input from being out of spec.

     

    TI makes a few chip based  and you can find some pre built boards on line too.  From $2 bucks to $20 or so depending on how many lines it supports.

     

    Like this one from sparkfun.

     

    If you've ever tried to connect a 3.3V device to a 5V system, you know what a challenge it can be. The SparkFun bi-directional logic level converter is a small device that safely steps down 5V signals to 3.3V AND steps up 3.3V to 5V at the same time. This level converter also works with 2.8V and 1.8V devices. What really separates this Logic level converter from our previous versions is that you can successfully set your high and low voltages and step up and down between them safely on the same channel. Each level converter has the capability of converting 4 pins on the high side to 4 pins on the low side with two inputs and two outputs provided for each side.

    The level converter is very easy to use. The board needs to be powered from the two voltages sources (high voltage and low voltage) that your system is using. High voltage (5V for example) to the 'HV' pin, low voltage (3.3V for example) to 'LV', and ground from the system to the 'GND' pin.

     

     

    Or Maybe something like this from digikey?  

    Customer would need to do his own diligence. 

     

     

    I also attached a older design we used back in the day.  It uses a TIB0106.  This was being used to hook up a Jlink at 3vdc to a NPX MO running on 5 volts.  There may be newer ones from TI .  The TIB0104 maybe cheaper but a board would need to be designed. It is worth looking at I guess.

    This board is no longer available.

     

     

     

    Best regards,

  • 0

    Thanks everyone for your prompt answers.  To be clear I am not looking for a long-term solution, just something to get us past an early prototype issue in order to meet a demo date.  I already have level shifters on other pins from this device, but they would not be particularly effective on these analog signals.

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