Why are N-Channel mosfets used here on the battery gauge lines?

[caphair]

This is from the iPhone 10, previous models didn't have mosfets on the gauge lines so I'm wondering why they're used now.

Is it so the phone can't boot with just a voltage present from external supply with gauche lines or?

(First attachment is from the iPhone 10 and the next is from an iPhone 6s)

[redwire]

Re: Why are N-Channel mosfets used here on the battery gauge lines?

I would say the iPhone 10 MCU is lower I/O voltage at 1.8V
The two Rohm RV1C002UN MOSFETs are used as level-translators for the battery pack serial comms.
They convert from 3.7V-4.3V serial data from the battery management IC down to 1.8V for the MCU I2C port, so they can talk to each other.

[caphair]

Re: Why are N-Channel mosfets used here on the battery gauge lines?

Thanks. Is a level translator the same as level shifting?

[redwire]

Re: Why are N-Channel mosfets used here on the battery gauge lines?

Yes, they mean the same thing.

[japlytic]

Re: Why are N-Channel mosfets used here on the battery gauge lines?

I've seen N-channel MOSFETs on power tool battery packs which serve as an overdischarge and overcurrent protection function.