ATX Version 3 Multi Rail Desktop Platform Power Supply

Design Guide

ID 336521
Date 11/01/2023
Document Table of Contents

Reliability – PS_ON# Toggle for S0ix Mode - REQUIRED

Computer can periodically wake from S0ix depending on operation system, installed software, user interaction and other design implementation. Such wakes can have impact not only to the PSU reliability, but also be a source of end user annoyance with PSU fan spinning on then off again.

In order to optimize desktop platform power consumption, Intel provides design recommendation to enable power supply PS_​ON# toggle on/off during S0 idle power mode (S0ix) to save both system and PSU power. The power supply PS_​ON# signal may toggle on/off every 180s (PSU to be on for up to 1s and off for 180s) when customer desktop designs implement S0 idle which is different from the legacy desktop platform design that PS_​ON# only toggles once when turned on. The S0ix mode is used in systems that use Alternative Low Power Modes. This on / off toggling comes from scheduled OS maintenance tasks that occur in the background that necessitate bringing the PC on in order to execute CPU instructions.

Although the periodicity for on/off toggling is non-deterministic, it can happen regularly after the system has entered the S0ix idle mode with PS_​ON# de-asserted. If the computer turns on/off every 180 seconds, the worst-case scenario would be 480 times in one day and 175,200 times in one year. The power supply needs to be able to handle this many cycles for the life of the power supply.

To have a better user experience, and avoid PSU fan acoustic noise annoyance, system and PSU designers should have at least two seconds delay time for the PSU fan to spin up after PS_​ON# assertion. A PSU is expected to support running at full load without any electrical, thermal components (i.e., IC, MOSFET, diode, transformer, inductor, capacitor, relay, fan, etc.) damaged or degraded during the period of time before the warranty expired. Due to the frequent PS_​ON# toggle on/off, system and PSU component’s reliability should be considered based on the days, months, or years of claimed warranty listed on product specification. This is also mentioned in Section 5.3.2.