Supervisor for battery-backed rails
The MAX817LESA+ from Analog Devices is a battery backup supervisory circuit that monitors a single voltage rail at a 4.65V threshold and asserts an active-low reset output. Packaged in the industry-standard 8-SOIC footprint, it integrates the backup-battery switchover logic and reset generation into a single surface-mount IC.
Threshold and timeout — what they mean for the board
The 4.65V threshold is tailored for 5V nominal supplies. At the trip point, the supervisor holds the processor in reset until the rail has recovered and stayed above threshold for at least 140ms. This prevents the MCU from attempting to boot during a glitch or brownout condition. With a single monitored voltage and an active-low, open-drain reset output, the MAX817LESA+ connects directly to the reset pin of most microcontrollers without needing an external pull-up. The reset timeout is internally fixed, so no external capacitor is required for timing.