The 2.9 V threshold sets the supervisory trip point: the MAX6466XR29+T asserts a reset when the monitored rail drops below 2.9 V and releases it after the 150 ms minimum timeout once the rail recovers — this delay prevents spurious resets on glitches or brown-out transients shorter than 150 ms.
Housed in a 3-lead SC-70, the part occupies roughly 2 mm × 2 mm of board area — the same footprint as a small-signal transistor, so it fits into tight regulator output sections or near the MCU reset pin without a dedicated supervisor zone.