Four-rail supervisor for multi-voltage boards
One channel has a fixed 3.08V threshold; the other three accept adjustable thresholds set by external resistor dividers, giving you flexibility to track 2.5V, 1.8V, 1.2V or any other common logic rail. The open-drain output stays asserted for a minimum of 140ms after all rails return to tolerance, ensuring the system microcontroller or FPGA sees a clean power-good signal before code execution starts.
Threshold selection and reset timing
The fixed 3.08V threshold suits a 3.3V rail with a typical undervoltage detect point around 3.0V. For the three adjustable channels, choose resistor values to set the trip point anywhere above the supervisor's internal reference. The 140ms minimum reset timeout gives low-speed or heavily decoupled supplies enough time to settle; if your system needs a longer delay, an external capacitor on the reset output can extend the pulse width. The open-drain output requires a pull-up resistor to the logic supply voltage of the downstream device.