Power Supply Ps_On Considerations - Intel 815EG Design Manual

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10.3

Power Supply PS_ON Considerations

• If a pulse on SLP_S3# or SLP_S5# is short enough (~ 10–100 mS) such that PS_ON is driven
active during the exponential decay of the power rails, a few power supplies may not be
designed to handle this short pulse condition. In this case, the power supply will not respond
to this event and never power back up. These power supplies would need to be unplugged and
re-plugged to bring the system back up. Power supplies not designed to handle this condition
must have their power rails decay to a certain voltage level before they can properly respond
to PS_ON. This level varies with affected power supply.
• The ATX spec does not specify a minimum pulse width on PS_ON de-assertion, which means
power supplies must be able to handle any pulse width. This issue can affect any power supply
(beyond ATX) with similar PS_ON circuitry. Due to variance in the decay of the core power
rails per platform, a single board or chipset silicon fix would be non-deterministic (may not
solve the issue in all cases).
• The platform designer must ensure that the power supply used with the platform is not
affected by this issue.
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Intel 815EG Chipset Platform Design Guide
I/O Controller Hub 2 (Intel® ICH2)
103