IO Pull-up vs Pull-down consumption

[Jose Xavier]

What does consume more power, IO pull-up or IO pull-down? Didn't find information about this on the product specification.

[Stefan Birnir Sverrisson]

Hi Jose

According to nRF51822 PS v3.1 section 8.23 pullup and pulldown resistors have a typical value of 13kohm. Therefore, if you have e.g. a button that connects a certain pin to ground when pressed, and the pin is configured as input with pullup, and you have supply power of 3.0 volts for the nRF51, then the current consumption is 3/13k=230uA when the button is pressed.

[Stefan Birnir Sverrisson]

ok, I understand. In your case this obviously has major influence on the battery life. What I would recommend then in your case is to connect an oscilloscope to the GPIO pin that you connect to the button, disable internal pull, and experiment with different external pullup resistors, if weaker pullup can actually remove noise from the pin in all situations that you can think of that can cause disturbance to that pin. Another option would be to add a circuit to your PCB that generates a short pulse when a button is pressed, which is adequately long to trigger a nRF51 event. This approach will be perhaps safer but will add some cost.