DC Output Current – REQUIRED - 2.01 - ID:336521 | ATX Version 3.0 Multi Rail Desktop Platform Power Supply

ATX Version 3.0 Multi Rail Desktop Platform Power Supply

Design Guide

ID	Date	Version	Classification
336521	02/01/2023		Public

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DC Output Current – REQUIRED

The below table summarizes the expected output transient step sizes for each output. All items in the below table are REQUIRED, unless specifically called out as RECOMMENDED.

Table 4-3. DC Output Transient Step Sizes

Output	Maximum Step Size (% of rated output amps)	Maximum Step Size (A)
+12V1DC ⁵	40% (Required)70% (Recommended)	-
+12V2DC ⁵	85% of CPU supported in Table 2-1 Table 2-1²	-
+12V3/4 ⁵	Steps from 100% à 300%⁴ 30% à 100% ³
+5VDC	30%	-
+3.3VDC	30%	-
-12VDC	-	0.1
+5VSB	-	0.5

Note:Example of how to use this table, for a rated +5 VDC output of 14A, the transient step would be 30% x 14 A = 4.2 A. Testing for a 4.2 A step size would result in testing starting at 9.8A going up to 14A.
12V2 rails are typically used for CPU power. CPU step size will have more updated values in the Power Supply Design Guide Addendum (# 621485) which will be used to determine the 85% value
12V3/V4 rails are typically used for PCIe* Add-in Card connectors. This recommendation is based on Chapter Chapter 3 where PCIe* Add-in Card needs are discussed. The step size will come from the amount of PCIe* Add-in Card power supported based on the size of the PSU in Table 3-2.For more detail reference the Desktop Platform Form Factor Power Supply Test Plan (Doc #338448)
If a power supply has multiple 12VHPWR connectors, Dynamic testing shall be done on each 12VHPWR connector. For more detail reference the Desktop Platform Form Factor Power Supply Test Plan (Doc #338448)
Power supplies that have one combined 12V rail shall perform Dynamic testing on the one 12V rail with multiple tests which simulate different system level workloads: 12V1 (total system), 12V2 (CPU Load), and 12V3/V4 (PCIe AIC).

Output voltages should remain within the regulation limits of Table 4-2, for instantaneous changes in load as specified in Table 4-4 and for the following conditions:

Simultaneous load steps on the +12 VDC, +5 VDC, and +3.3 VDC outputs (all steps occurring in the same direction)
Load-changing repetition rate of 50 Hz to 10 kHz
AC input range per Section Section 2.1 and Capacitive loading per Table 4-7

The transient load slew rate is defined in Table 4-4 based on whether the PSU supports the PCIe* 12VHPWR Connectors. This usually can be correlated to the PSU’s Rated Wattage, which is listed as a guidance.

Table 4-4. DC Output Transient Slew Rate

Output	PSU without PCIe* 12VHPWR Connectors (Recommended Size ≤450 Watts)	PSU with PCIe* 12VHPWR Connector(Recommended Size >450 Watts)
All +12V	2.5 A/µs	5.0 A/µs
+5V	1.0 A/µs	1.0 A/µs
+3.3V	1.0 A/µs	1.0 A/µs
+5VSB	0.1 A/µs	0.1 A/µs
-12V	0.1 A/µs	0.1 A/µs