ATX Version 3 Multi Rail Desktop Platform Power Supply

Design Guide

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


This optional sideband signal functions as a “Power Good” indicator from the Add-in Card to the PSU. When this signal is asserted, the Add-in Card confirms that local power rails on the Add-in Card lie within their operating voltage limits. This signal can provide a fault detection alert from the Add-in Cards to the PSU, which can provide the PSU an opportunity for protective measures.

If CARD_​PWR_​STABLE signal is supported by an Add-in Card, the signal it will be implemented in an open collector / open-drain configuration.

When implemented in the power supply, the signal must be tied to a 4.7 kΩ pull-up resistor to +3.3V. The PSU must monitor the state of the CARD_​PWR_​STABLE with a high impedance 3.3V logic compatible device input.

The Add-in Card will set this signal to Open (high impedance) whenever its local power rails that are critical to correct operation are within their operating limits. When the Add-in Card directly drives this signal low (0 / Ground), any of its local power rails are outside of their operating limits results in a fault for the Add-in Card. The Add-in Card must drive this signal low for at least 100 ms or as long as the input power stays outside of the voltage specification detailed in Table 3-5: Auxiliary Power Connectors Power Supply Rail Requirements - +12V Only in Section Section 3.2 of this document. When the voltage returns to within correct operating ranges and the fault is done, the signal will change to open (high impedance). If or when a fault is corrected the Add-in Card again sets this signal to open (high impedance).

Support for this optional sideband signal does not rely on any of the other sideband signals defined for the 12V-2x6 connector and can be implemented independently of other of these sideband signals.