Maxim > Design Support > Technical Documents > Application Notes > Circuit Protection > APP 5555
Maxim > Design Support > Technical Documents > Application Notes > Power-Supply Circuits > APP 5555
Keywords: analog design, power-on-reset, POR, reliable, power supplies, power supply slopes,
hysteresis, safety, analog resistor capacitor, RC, time constants, momentary voltage drops, timers
APPLICATION NOTE 5555
Scaling Power-Supply Slopes with a Reliable
Power-On Reset (POR)
By: Bill Laumeister, Strategic Applications Engineer
Jun 12, 2013
Abstract: 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.
A similar version of this article appeared in the May 2013 issue of Electronic Science Korea magazine.
Introduction
Power-on reset (POR) usually places devices in known, ready-to-operate configurations. POR thus
sounds 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.
Power Lines and Mountain Cliffs
We start our discussion with a metaphor: a valley or plain where we walk up and down mountains,
illustrated by the colored lines in Figure 1.
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