Using AIN pin as GPIO on nRF52820

[janvb]

Hi, on the nRF52820-QDAA I am using pin 5 AIN3 /  P0.05  as an GPIO output to drive a LED (active low).

This does not work in the software, when I drive the pin high with nrf_gpio_pin_set, the pin goes to 2V instead of VDD.

Probably there is something wrong in the configuration, but I looked everywhere and cannot find any setting that I should change to make it work.

[Susheel Nuguru]

This does not work in the software, when I drive the pin high with nrf_gpio_pin_set, the pin goes to 2V instead of VDD.

What is the value of VDD you are using? Assuming that this is a custom board, it is hard to say what is limiting the output voltage. Also are you using high drive setting ? Did you get your schematics and layout files reviewed? Are you sure there is nothing in the hardware design or build that might cause the issues?

[janvb]

VDD is 1.8V, the battery powering the system is at 3.8V and connected to the VDDH pin. As the anodes of the LEDs are also connected to VDDH, I now understand that the problem is that the LED threshold voltage is smaller than VDDH-VDD, so that current is flowing through the LED into the pin when high.  What is the best way to resolve this?  

Can I use an open drain output?  But in that case the pin voltage will rise above VDD when the pin is high, so that is violating the max ratings.

[Susheel Nuguru]

janvb said:

I now understand that the problem is that the LED threshold voltage is smaller than VDDH-VDD, so that current is flowing through the LED into the pin when high.  What is the best way to resolve this?  

You should probably fix this first so that extra current does not flow back to the pin