Hey @alp,
If you want to do the FOC control you do not really need the third current sense. You can have it for back emf and similar applications where the current does not pass through all the phases at the same time.
For sinusoidal currents you can always find the third current by calculating:
ic = 0 -ia -ib
We will be supporting both two and three current so you can choose which one suites you more.
Three currents is more robust because you have more measurements and on average less error.
Regarding the 3btns on one pin. Honestly this is all an ok option but I am not 100% sure that simplefoc will support this natively. We will try to support low-side (3x or 2x), inline and high side.
But low side with one shunt requires a very high degree of synchronisation and it is not at all inpossible but makes things even more hardware specific than just low-side sensing. So i would suggest you to separate these pins so that you can read them at the same time.
Btw, when you put as requirement that the btns should not be on at the same time, for the center aligned pwm modulation this will almost never be the case. But this is not really a requirement, more of them can be open at the same time, but not all low or high side ones.
There is a nice thread where @robin2906 well explained the problems of this approach:
https://community.simplefoc.com/t/advice-on-current-sensing-for-new-board-design/206/40?u=antun_skuric
I hope I didn’t confuse you with my post. 