How to design circuit board with RAK3172 to optimize low current consumption?

I am designing my own circuit board with the power used from the battery.
Therefore, the energy-saving factor is put on top.

I have some questions that need help from everyone experienced in this matter.

Unused pins should be in the input or output state.
In the case of input, it should be pullup, pulldown, or floating.
In the case of output, it should be set as high or low.

With the I2C pins, can I use the internal pull-up resistor for I2C communication?
Would using an internal or an external pull-up resistor be more power efficient?

If I have an input pin, should I use active LOW (normal pull-up) or HIGH (normal pull-down) to save more power?

If I have an output pin that drives the led, I should connect it to 3.3V through a resistor and control the other terminal.
Or controlled directly by the current output from the pins of rak3172

Thank you.

Hi @Nam ,

Most of your questions can be answered by this application note from STMicroelectronics -

Low power consumption (if related to pins) is fundamentally affected by how the current and voltage is managed. For example on I2C pins, more efficient will be the internal pull-up since it is higher than usual external pull-ups we use like 10k and 4.7k. However high resistor pull-ups will make the I2C bus not strong enough to change to a stable state. As they say, electronics design is an art of compromise - low power, thermals, noise, EMI compliance, etc.

Btw, I saw your RAK3172 board. Looking forward for the success of that (and more orders of RAK3172) :grin: :raised_hands: :rocket:

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Thank you, the material is very helpful.