ATX Version 3.0 Multi Rail Desktop Platform Power Supply
Design Guide
+5V DC / +3.3V DC Power Sequencing - REQUIRED
The +12V1 DC / +12V2 DC and +5 VDC output levels must be equal to or greater than the +3.3 VDC output at all times during power-up and normal operation. The time between any output of +12V1 DC / +12V2 DC and +5 VDC reaching its minimum in-regulation level and +3.3 VDC reaching its minimum in-regulation level must be ≤ 20 ms as shown in Figure 4-2.
Figure 4-2: Power Supply Timing