Problem with "saadc" example (nRF52840 PDK)

[Maxime]

Hi there,

I'm testing the "saadc" example : <InstallFolder>\examples\peripheral\saadc

I haven't changed the code.

To do this, I use the nRF52840 with SDK 14.2 and s140 softdevice.

The nRF52840 is powered by a USB cable.

To observe the values, I use a terminal emulator (PuTTY). Then, I use an external power supply on AIN0 that I vary between 0 and 3.6V to observe the numerical value on the console.

Everything is going well, until my measured voltage exceeds 2.1V. You can see this in the next capture:

I would like the curve to remain linear up to 3.6V. Do you have an idea for solving my problem?

Thank you in advance for your answers!

[ovrebekk]

Hi Maxime

What is the supply voltage on the chip?

The voltage on any GPIO can not exceed VDD + 0.3V, as there are ESD protection diodes on the pins that will start conducting at this voltage. 

Your results make sense if you have a VDD voltage of 1.8V, as you would expect the diodes to start conducting around 2.1V. 

To solve this you would have to use a voltage divider externally, to make sure that the input voltage on the pin stays below VDD + 0.3V. 

Best regards
Torbjørn Øvrebekk

[Maxime]

Thank you very much, I think you're right.

I will try and confirm the resolution of my problem.

[Maxime]

It works. Thank you very much!

[ovrebekk]

I am happy to help