ATX Version 3.0 Multi Rail Desktop Platform Power Supply

Design Guide

ID 336521
Date 01/02/2022
Version 2.0
Public
Document Table of Contents

PSU Power Excursion

Based on the power budgets in Table 3-2 and peak power of both the Processor detailed in Table 2-1 and the PCIe* Add-in Cards in Section Section 3.1, the following Peak Power Requirements are defined for the Power Supply. The peak time for each power level is defined in Table 3-3. The PCIe Add-in cards power excursion are only designed for the new 12VHPWR connector, therefore the table is split into two different power levels where it is expected that power supplies greater than 450 watts will have at least one 12VHPWR connector.

Table 3-3: PCIe* AIC and PSU Power Budget used for Peak Power Excursion

Power Excursion % of PSU Rated Size

PSU ≤ 450 Watts & PSUs without 12VHPWR Connector

Power Excursion % of PSU Rated Size

PSU > 450 Watts & 12VHPWR Connector present

Time for Power Excursion (TE)

Testing Duty Cycle

100%

100%

Infinite

--

110%

120%

100 ms

50%

135%

160%

10 ms

25%

145%

180%

1 ms

20%

150%

200%

100 µs

10%

Note:Peak Power defined in this table correspond to Platform Level Power Budgets described in Table 3-2 if CPU or Rest of Platform power is reduced from Table 3-2 to reduce PSU size, then custom Power Excursion % of PSU rated size must also be calculated.

The Testing Duty Cycle is not defined in the PCIe* CEM Gen 5.0 ECN, but it must be defined to create a test criteria specific to a power supply. The Testing Duty Cycle defines the percentage of time the Power Excursion value peaks with the remainder of the time defined as a Time_​Constant (TC). The Power Level defined is to have the RMS value during this Dynamic Load test to be the Rated Wattage of the Power Supply. shows an example of how the testing criteria for power excursions of 1000 Watt Power Supply using an RMS value to average the rated power of a power supply. This calculation is the same as what is described in the PCIe* CEM Gen 5 Power Excursion ECN. For all power supplies with a rated wattage different than 1000 watts a similar RMS calculation needs to be performed.

Figure 3-2: Duty Cycle Definition

image3.png

Table 3-4: Duty Cycle Example Test Criteria for a 1000W PSU – RMS

Duty Cycle

Time for Power Excursion (TE)

Time Constant (TC)

Power @ TE

Power @ TC

10%

100 µs

900 µs

2000 W

817 W

20%

1 ms

4 ms

1800 W

663 W

25%

10 ms

30 ms

1600 W

693 W

50%

100 ms

100 ms

1200 W

749 W

  1. The Capacitive Load mentioned in Table 4-7 is expected to be applied to this test scenario.
  2. Total Test time for each Power Excursion testing time is expected to last until thermal saturation occurs in the PSU.
  3. More details about test time for each row above and formulas to calculate TC and TE power values for different PSU sizes will be detailed in the “Desktop Platform Form Factor Power Supply Test Plan – Doc #338448