What the TPS3809J25DBVTG4 does on the board
The output is push-pull, active low, so it drives the reset pin directly without an external pull-up resistor.
The 2.25 V threshold is the trip point: when the monitored voltage drops below this level, the reset output asserts. For a 2.5 V logic rail, this gives about 250 mV of margin before the supervisor triggers — enough headroom to catch a sagging supply without nuisance resets on ripple. The 120 ms minimum reset timeout is a fixed delay, not adjustable. It is long enough for most crystal oscillators and PLLs to lock, but if your processor needs a longer hold time, you would need a different supervisor with a programmable or longer timeout period.
Housed in a SOT-23-3 package, this is a three-pin device — supply, ground, and reset output.