Not sure what you mean by the 'boost circuit'
Asicboost is a modification of the internal ASIC hashing function to produce more nonces.
Thus it's simply part of the internals of the BM1397 i.e. a change in the silicon design of the BM1397 vs pre S9 chips.
Hi Kano, This chip is located below the "boost circuit" zone according to the manual. I'm now leaning towards some type of linear regualtor but still guessing at this point.
https://drive.google.com/file/d/1vZ-mMlRZMI8XntUU3hC0SJa4MF-a6OjP/view?usp=sharing