What the 4.55 V threshold means for a 5 V rail
The MAX815NCSA+ monitors a single 5 V supply and asserts a reset when the voltage drops to 4.55 V. That threshold sits at 91% of nominal — early enough to hold the processor in reset before the supply falls out of regulation, but late enough that a lightly loaded 5 V rail with ±5% tolerance never triggers a nuisance reset during normal ripple. The 140 ms minimum reset timeout gives the supply time to recover from a brown-out before the processor tries to re-execute from an undefined state. For a system with a bulk capacitor sized for 10 ms hold-up, the extra margin means the supervisor does not release reset until the rail is stable.
Output type and system integration
The active-low reset output is push-pull / totem-pole, so it drives the processor reset pin directly without an external pull-up resistor. This saves a component and eliminates the risk of the reset line floating during power-up if the pull-up rail comes up late. Because the output is push-pull, it can sink and source current — useful when the reset line also drives a status LED or a reset input on multiple peripherals on the same bus.