Scaling Power-Supply Slopes with a Reliable Power-On Reset (POR)

This application note discusses designing power-on reset (POR) circuits for a wide range of voltage conditions.  After reviewing why a POR typically fails, this application note covers the best ways to make the POR work safely, to test the POR, and to implement a design strategy- all with an eye on making the POR function more reliably. 

Power-on reset (POR) usually places devices in known, ready-to-operate configurations. POR thus sunds simple, and in the vast majority of cases, it works well. But when it fails, POR can trigger a series of critical events and eventually cause a catastrophe. In this application note, we explore the world of POR, its variables, “Murphy’s Law”,1 and the “gotchas”2 that most of us have had to struggle through sometime in our career. Despite the best POR design for an application, ultimately, the end user also bears some responsibility for ensuring that the POR function remains reliable.