Adding Hysteresis to CPU Supervisor Voltage Sense Inputs Monitoring Upstream Voltage Supplies for Power-Fail Warnings

Abstract: One of the most important features in any embedded design is ensuring that important data is properly saved and the system reaches a safe/known state as power is failing. A CPU supervisor with a voltage sense input can monitor an upstream voltage supply and provide a warning signal to the microprocessor that signifies that power is failing. This allows the microprocessor time to save critical data and reach a safe/known state before the CPU supervisor, which will also be monitoring the processor's power supply, resets the processor. This application note shows how to add hysteresis to the upstream voltage supply's trip level, which prevents the power-fail warning signal from chattering due to noise. This circuit provides a great tool for producing a sophisticated power-supply monitoring system that will help to produce a robust embedded design.