Voltage drop on GPIO pins at higher loads

[Jon]

Hi.

I'm currently testing the GPIO pins in regards to current draw on the nrf9160 development kit and I noticed that there was about a ~0.15V voltage drop on the GPIO pin when it was connected to ground through a 1k resistor, giving a current draw of 3mA.

Is this expected behaviour on the nrf9160? I configured the pin to run in High drive mode, and with no load connected the output is 3.0V as expected.

I see that according to the datasheet the output high voltage is specified as minimum of Vdd-0.4 and maximum of Vdd. Does that mean that the voltage output can vary between 2.6-3.0V in high mode depending on the load?

[ketiljo]

There will be some voltage drop in the GPIO depending on the current draw. When you draw  a current of 5 mA in high drive wuth 2.7 V supply voltage, you can expect a max voltage drop of 0.4 V. 

This is because the GPIO internal resistance. 

[Jon]

Alright, that's good to know. So can I expect the voltage to drop linearly in relation to the current? Can I see somewhere in the datasheet what typical values for the resistances in the GPIOs are?

[ketiljo]

Yes, the resistance is the same on the same device It's not stated in the datasheet. It will vary with chip to chip and temperature.