Intel ATX12VO Guide

Document Number: 613768
ATX12VO (12V Only) Desktop
Power Supply
Design Guide
Revision 2.01
January 2023

2 613768
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613768 3
Contents
1Introduction.................................................................................................... 11
1.1 Power Supplies and Alternative Low Power Mode ...................................... 11
1.2 System Power Telemetry Feature............................................................ 12
1.3 References........................................................................................... 12
1.4 Terminology ......................................................................................... 13
2Processor Configurations .................................................................................. 16
2.1 Processor Configurations (Recommended) ............................................... 16
2.2 High End Desktop Market Processor Considerations................................... 16
2.2.1 Modular Power Supply Connectors ............................................. 17
2.2.2 Overclocking Recommendations ................................................ 18
3PCI Express* Add-in Card Considerations ........................................................... 19
3.1 PCIe* Add-in Card Power Excursions ....................................................... 19
3.1.1 PCIe* Add-in-Card and PSU Power Budgets ................................ 21
3.1.2 PSU Power Excursion ............................................................... 23
3.2 PCIe* AIC Auxiliary Power Connectors..................................................... 24
3.3 PCIe* Add-in-Card Auxiliary Power Connectors Sideband Signals ................ 25
3.3.1 Sense1 / Sense0 (Required) ..................................................... 25
3.3.2 CARD_PWR_STABLE (Optional) ................................................. 26
3.3.3 CARD_CBL_PRES# (Optional) ................................................... 27
3.3.4 Sideband Signals DC Specifications (Required) ............................ 28
4Electrical ........................................................................................................ 29
4.1 AC Input – REQUIRED ........................................................................... 29
4.1.1Input Over Current Protection (Required) ................................... 29
4.1.2 Inrush Current (Required) ........................................................ 29
4.1.3 Input Under Voltage (Required)................................................. 29
4.2 DC Output (Required)............................................................................ 30
4.2.1 DC Voltage Regulation (Required).............................................. 30
4.2.2 DC Output Current (Required)................................................... 30
4.2.3 Remote Sensing (Optional) ....................................................... 31
4.2.4 Other Low Power System Requirements (Required) ..................... 31
4.2.5 Output Ripple Noise (Required) ................................................. 32
4.2.6 Capacitive Load (Recommended)............................................... 33
4.2.7 Closed Loop Stability (Required)................................................ 33
4.2.8 Multiple 12V Rail Power Sequencing (Required) ........................... 34
4.2.9 Voltage Hold-Up Time (Required) .............................................. 34
4.3 Timing, Housekeeping, and Control (Required) ......................................... 34
4.3.1 PWR_OK (Required)................................................................. 35
4.3.2 PS_ON# (Required) ................................................................. 35
4.3.3 +12VSB (Required).................................................................. 37
4.3.4 Power-On Time (Required)........................................................ 38
4.3.5 Rise Time (Required) ............................................................... 38
4.3.6 Overshoot at Turn-On / Turn-Off (Required) ............................... 39
4.3.7 I_PSU% Signal (Required) ........................................................ 39
4.4 Reset After Shutdown............................................................................ 44
4.4.1 +12VSB at Power-Down (Required) ........................................... 44
4.4.2 +12VSB Fall Time (Recommended)............................................ 44

4 613768
4.5 Output Protection.................................................................................. 45
4.5.1 Over Voltage Protection (OVP) (Required)................................... 45
4.5.2 Short Circuit Protection (SCP) (Required) ................................... 45
4.5.3 No-Load Situation (Required) .................................................... 45
4.5.4 Over Current Protection (OCP) (Required) .................................. 45
4.5.5 Over Temperature Protection (OTP) (Required) ........................... 46
4.5.6 Output Bypass (Required)......................................................... 46
4.5.7 Separate Current Limit for 12V2 (Optional)................................. 46
4.5.8 Overall Power Supply Efficiency Levels ....................................... 46
4.5.9 Power Supply Efficiency for Energy Regulations - ENERGY STAR* and
CEC PC Computers with High Expandability Score (Recommended) 47
5Mechanical...................................................................................................... 49
5.1 Labeling and Marking (Recommended) .................................................... 49
5.2 Connectors (Required)........................................................................... 50
5.2.1 AC Connector.......................................................................... 50
5.2.2 DC Connectors ........................................................................ 50
5.3 Connector from Motherboard to Storage Devices – Reference..................... 62
5.3.1 Motherboard Connector ............................................................ 62
5.3.2 Serial ATA Connectors (Reference) ............................................ 67
5.4 Airflow and Fans (Recommended) ........................................................... 69
5.4.1 Fan Location and Direction........................................................ 69
5.4.2 Fan Size and Speed ................................................................. 69
5.4.3 Venting .................................................................................. 69
6Acoustics ........................................................................................................ 71
7Environmental................................................................................................. 72
7.1 Temperature (Recommended) ................................................................ 72
7.2 Thermal Shock (Shipping)...................................................................... 72
7.3 Humidity (Recommended) ..................................................................... 72
7.4 Altitude (Recommended) ....................................................................... 72
7.5Mechanical Shock (Recommended) ......................................................... 72
7.6 Random Vibration (Recommended) ......................................................... 73
8Electromagnetic Compatibility ........................................................................... 74
8.1 Emissions (Required)............................................................................. 74
8.2 Immunity (Required)............................................................................. 74
8.3 Input Line Current Harmonic Content (Optional) ....................................... 74
8.4 Magnetic Leakage Field (Required).......................................................... 74
8.5 Voltage Fluctuations and Flicker (Required).............................................. 75
9Safety ............................................................................................................ 76
9.1 North America (Required) ...................................................................... 76
9.2 International (Required) ........................................................................ 76
9.3 Proscribed Materials (Required) .............................................................. 77
9.4 Catastrophic Failure Protection (Recommended) ....................................... 77
10 Reliability ....................................................................................................... 78
10.1 Reliability (Recommended) .................................................................... 78
10.2 Reliability – PS_ON# Toggle for S0ix Mode (Required)............................... 78
11 CFX12V Specific Guidelines 2.0.......................................................................... 79
11.1 Physical Dimensions (Required) .............................................................. 79

613768 5
12 LFX12V Specific Guidelines 2.0 .......................................................................... 80
12.1 Physical Dimensions (Required) .............................................................. 80
13 ATX12V Specific Guidelines 3.0 ......................................................................... 83
14 SFX12V Specific Guidelines 4.0.......................................................................... 85
14.1 Lower Profile Package – Physical Dimensions (Required)............................ 85
14.2 Fan Requirements (Required) ................................................................. 85
14.3 Top Fan Mount Package – Physical Dimensions (Required) ......................... 87
14.4 Fan Requirements (Required) ................................................................. 87
14.5 Reduced Depth Top Mount Fan – Physical Dimensions (Required) ............... 89
14.6 Fan Requirements (Required) ................................................................. 89
14.7 Standard SFX Profile Package – Physical Dimensions (Required) ................. 91
14.8 Fan Requirements (Required) ................................................................. 91
14.9 PS3 Form Factor – Physical Dimensions (Required) ................................... 93
14.10 Fan Requirements (Required) ................................................................. 93
15 TFX12V Specific Guidelines 3.0.......................................................................... 95
15.1 Physical Dimensions (Required) .............................................................. 95
15.2 Mounting Options (Recommended).......................................................... 97
15.3 Chassis Requirements (Recommended) ................................................... 98
16 Flex ATX Specific Guidelines 2.0 .......................................................................100
16.1 Physical Dimensions (Required) .............................................................100
Figures
Figure 3-1: PCI Express* CEM Add-in-Card Power Excursion Limits Chart ............... 21
Figure 3-2: Duty Cycle Definition....................................................................... 24
Figure 4-1: Differential Noise Test Setup ............................................................ 33
Figure 4-2: Power on Timing ............................................................................. 34
Figure 4-3: PS_ON# Signal Characteristics ......................................................... 37
Figure 4-4: +12VSB Power on Timing versus VAC................................................ 38
Figure 4-5: Rise Time Characteristics ................................................................. 39
Figure 4-6: I_PSU% Delay Time Diagram ........................................................... 41
Figure 4-7: Recommended Circuit Diagram for I_PSU% signal inside PSU............... 42
Figure 4-8: 12VSB Fall Time ............................................................................. 44
Figure 5-1: 12VHPWR Connector Labeling Example.............................................. 50
Figure 5-2: 4.2 mm Power Header 10 pin Main Power - Pin Locations..................... 51
Figure 5-3: 4.2 mm Power Header 10 pin Main Power – Motherboard Connector, PC
Board Layout with Dimensions .................................................................... 52
Figure 5-4: 12VHPWR Cable Plug Connector........................................................ 58
Figure 5-5: 12VHPWR Cable Assembly ............................................................... 59
Figure 5-6: 12VHPWR Cable Plug Connection Recommendation ............................. 60
Figure 5-7: 3 mm SATA Power 4 Pin MB Header – Motherboard Connector Diagram
(Pin Locations and Latch Location)............................................................... 63
Figure 5-8: 3 mm SATA Power 4 Pin MB Header – Recommended PCB Layout (Top
Layer View) .............................................................................................. 63
Figure 5-9: 3 mm SATA Power 4 Pin Cable Connector – Key and Pin Locations ........ 64
Figure 5-10: 3 mm SATA Power 6 Pin MB Header – Recommended PCB Layout (Top
Layer View) .............................................................................................. 65
Figure 5-11: 3 mm SATA Power 6 Pin MB Header – Keying and Pin Locations.......... 66

6 613768
Figure 5-12: 3 mm SATA Power 6 pin/4 SATA Device Cable Diagram (Connector Top
View) ....................................................................................................... 66
Figure 5-13: 3 mm SATA Power 6 Pin Cable Connector – Traditional Cable Diagram. 66
Figure 5-14: 3 mm SATA Power 6 Pin Cable Connector – Key and Pin Locations
(Bottom View)........................................................................................... 67
Figure 5-15: Serial ATA Power Connector ........................................................... 68
Figure 11-1: CFX12V Mechanical Outline ............................................................ 79
Figure 12-1: LFX 12V Mechanical Outline ............................................................ 80
Figure 12-2: LFX 12V Mechanical Details ............................................................ 81
Figure 12-3: LFX 12V PSU Slot Feature Detail ..................................................... 81
Figure 12-4: LFX 12V Recommended Chassis Tab Feature .................................... 82
Figure 13-1: ATX12V Power Supply Dimensions for Chassis Not Requiring Top Venting
83
Figure 13-2: ATX12V Power Supply Dimensions for Chassis that Require Top Venting
84
Figure 14-1: SFX12V 40 mm Profile Mechanical Outline........................................ 86
Figure 14-2: SFX121V Chassis Cutout ................................................................ 86
Figure 14-3: SFX12V Top Mount Fan Profile Mechanical Outline ............................. 88
Figure 14-4: SFX12V Chassis Cutout .................................................................. 89
Figure 14-5: SFX12V Recessed Fan Mounting ...................................................... 89
Figure 14-6: SFX12V Reduced Depth Top Mount Fan Profile Mechanical Outline....... 90
Figure 14-7: SFX12V Top Mount Fan, Inside enclosure Mechanical Outline (Possible
Larger Fan)............................................................................................... 91
Figure 14-8: SFX12V Chassis Cutout .................................................................. 91
Figure 14-9: SFX12V 60 mm Mechanical Outline.................................................. 92
Figure 14-10: SFX12V Chassis Cutout ................................................................ 93
Figure 14-11: SFX12V PS3 Mechanical Outline .................................................... 94
Figure 15-1: TFX12V Mechanical Outline............................................................. 95
Figure 15-2: TFX12V Dimensions and Recommended Feature Placements (Not to
Scale) ...................................................................................................... 96
Figure 15-3: TFX12V Power Supply Mounting Slot Detail....................................... 97
Figure 15-4: TFX12V Fan Right and Fan Left Orientations of Power Supply in Chassis98
Figure 15-5: Suggested TFX12V Chassis Cutout .................................................. 98
Figure 15-6: TFX12V Suggested Mounting Tab (Chassis Feature)........................... 99
Figure 16-1: Flex ATX Mechanical Outline ..........................................................100
Figure 16-2: Flex ATX Dimensions and Recommended Feature Placements (Not to
Scale) .....................................................................................................101
Tables
Table 1-1: Conventions and Terminology ............................................................ 14
Table 1-2: Support Terminology ........................................................................ 15
Table 2-1: Processor Configurations – 12V2 Current ............................................ 16
Table 3-1: PCI Express CEM Add-in Card Power Excursion Limits Table45 ................ 20
Table 3-2: PCIe* AIC and PSU Power Budget used for Peak Power Excursion Test
Cases....................................................................................................... 22
Table 3-3: PCIe* AIC and PSU Power Budget used for Peak Power Excursion .......... 23
Table 3-4: Duty Cycle Example Test Criteria for a 1000W PSU – RMS..................... 24
Table 3-5: Auxiliary Power Connectors Power Supply Rail Requirements - +12V Only25
Table 3-6: PCI Express* 12VHPWR Connector Power Limits .................................. 26
Table 3-7: PCI Express* 12VHPWR Connector – Sideband Signal DC Specifications.. 28
Table 4-1: AC Input Line Requirements .............................................................. 29
Table 4-2: DC Output Voltage Regulation............................................................ 30
Table 4-3: DC Output Transient Step Sizes ......................................................... 30

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Table 4-4: DC Output Transient Slew Rate .......................................................... 31
Table 4-5: Required System DC and AC Power Consumption................................. 32
Table 4-6: DC Output Noise/Ripple .................................................................... 32
Table 4-7: Output Capacitive Loads ................................................................... 33
Table 4-8: Power Supply Timing ........................................................................ 34
Table 4-9: PWR_OK Signal Characteristics .......................................................... 35
Table 4-10: PS_ON# Signal Characteristics......................................................... 36
Table 4-11: I_PSU% Signal Characteristics ......................................................... 39
Table 4-12: PCIE AIC and PSU Power Budget used for Peak Power Excursion .......... 43
Table 4-13: Duty Cycle Example Test Criteria for a 750W PSU – RMS..................... 43
Table 4-14: Duty Cycle Example Test Criteria for a 1000W PSU – RMS ................... 43
Table 4-15: Over Voltage Protection................................................................... 45
Table 4-16: Efficiency Load Minimum Requirements............................................. 46
Table 4-17: Low Load Efficiency Requirements Depending on Overall PSU Size........ 47
Table 4-18: 10W Load Condition (Value in Amps for PSU ≤ 500 Watts) .................. 47
Table 4-19: ENERGY STAR* Efficiency versus Load .............................................. 48
Table 4-20: CEC PC Computers with High Expandability Computers1- Efficiency versus
Load 48
Table 5-1: 4.2 mm Power Header Main Power Connector Part Numbers.................. 50
Table 5-2: Main Power Connector Pinout............................................................. 53
Table 5-3: Extra Board Connector – Required vs. Optional .................................... 54
Table 5-4: Extra Board Power Connector 6 Pin Connector Pinout............................ 54
Table 5-5: +12V Power 4 pin Connector Pinout ................................................... 54
Table 5-6: +12V Power 8 pin Connector Pinout ................................................... 55
Table 5-7: PCIe* 2x3 Auxiliary Power Connector Pin Assignment (75 Watts) ........... 55
Table 5-8: PCIe* 2x4 Auxiliary Power Connector Pin Assignment (150 Watts) ......... 56
Table 5-9: PCIe* 2x4 Auxiliary Power Connector Sense Pin Decoding by AIC........... 57
Table 5-10: PCIe* 12VHPWR Auxiliary Power Connector Pin Assignment (600 Watts)61
Table 5-11: Peripheral Connector Pinout............................................................. 61
Table 5-12: 3 mm SATA Power 4 Pin Connector Part Numbers .............................. 62
Table 5-13: SATA MB Power 4 Pin Connector Pinout............................................. 63
Table 5-14: 2 SATA Power Cable Part Numbers ................................................... 64
Table 5-15: 3 mm SATA Power 6 Pin Connector Part Numbers .............................. 65
Table 5-16: +12 V Power 6 Pin Connector Pinout................................................. 65
Table 5-17: SATA Power Cable Supporting 4 SATA Devices Part Numbers............... 67
Table 5-18: Serial ATA Power Connector Pinout ................................................... 68
Table 6-1: Recommended Power Supply Acoustic Targets..................................... 71
Table 8-1: EMC Requirement by Country ............................................................ 74

8 613768
Revision History
Document
Number
Revision
Number Description Revision Date
613768
0.9 •Initial version May 2019
1.0
•Section 2.1 – Added reference of PSU Addendum for all future
processor support.
•Table 4-6 – Updated 12VSB Ripple and Noise p-pV value to
match all other 12V Rails.
•Table 4-8 – Added note of where T0 is referenced.
•Section 4.5.9– Updated link of current ENERGY STAR*
Computers specification to version 8.0.
•Table 5-1 – Updated pin 10.
•Section 5.3 – Explained 4 pin and 6 pin SATA Power
connection in detail
•Changed all wording for Alternative Sleep Mode to Alternative
Low Power Mode (Although they both reference the same
power state, ALPM is more generic).
May 2020
1.01
•Section 5.2.2.1 – Updated the part number for CviLux*.
Updated Figure 5-3 to provide more clarification on the
connector.
November
2020
1.02
•Section 4.2.3 – Added extra clarity for use of remote sensing
•Section 5.2.2.1 – Updated the part number for Lotes*.
Provided clarification about Remote Sensing for the
connector.
•Added Figure 14-7 (Different Fan Option for SFX form factor)
February
2021
613768 1.1
•Added Section 1.2– System Power Telemetry Feature
•Table 4-17 – Low Load Efficiency previous required levels
moved to recommended and new required level is added
•Added Section 4.3.7– System Power (Psys) entire section is
new
•Section 5.1 – Label of all PSUs should state revision of the
specification that it meets
•Table 5-2: Main Power Connector Pinout – Pin 5 is now
defined
March
2022
613768 2.0
•Updated text for clarity in Section 1: Introduction
•Updated Section1.1 added second reference for ALPM in
Section 4.3.2
•Added new Reference Documentations to list in Section 1.3
•Updated Table 2-1: Processor Configurations – 12V2 Current
and reference text for Processors
•Updated Section 2.2 for accuracy and clarity
•Added ALL of Chapter 3– PCIe* AIC Consideration
•Updated Section 4.2.1 and Table 4-2 - DC Voltage lower
voltage range is changed to 11.2 Volts.
•Updated DC Output current – Slew rate is increased to meet
PCIe CEM requirements, along with max step size Section
4.2.2
March
2022

613768 9
Document
Number
Revision
Number Description Revision Date
•Table 4-4 added Slew Rate changes based on PSU size
•Added last sentence in Section 4.2.6 for clarification
•added about PSU must be able to resume quickly from fast
change in PS_ON# signal re-assertion in Section 4.3.2 last
paragraph
•Section 4.3.3 - PSUs 1200 watts or larger to have 12VSB rail
of 3.0 Amps or larger
•Added last sentence to describe when this section would be
needed in Section 4.5.7
•Added mention for label of all PSUs should state revision of
the specification that it meets and 12VHPWR label for power
level supported in Section 5.1
•Added PCIe* Add-in Card Connector section increased detail
for all 3 connector options including new 12VHPWR connector
in Section 5.2.2.4
•Changed table at beginning of each section to represent new
mechanical size Specification Revision in Chapter 11, 12, 13,
14, 15, and 16
613768 2.01
•Changed top row from 165W to 150W and associated power
values to correspond to latest updates in the PSU Design
Guide Addendum document Table 2-1
•Updated Duty Cycle for Peak Events change to match the PSU
Test Plan document in Table 3-3.
•Updated Whole table updated related to Duty Cycle for Peak
Events change to match the PSU Test Plan document Table
3-4
•Added Note #3 in Table 4-3 - that references Dynamic Mode
testing for each 12VHPWR Connector in the system
•Changed word “Rated” to “Recommended” in the top row of
the table in Table 4-4
•Removed reference to external document in Table 4-10 –to
Section 10.2, which already covered the items listed in this
document.
•Updated Table 4-12 - Duty Cycle for Peak Events changed to
match the PSU Test Plan document
•Updated Table 4-13 and Table 4-14 - Whole table updated
related to Duty Cycle for Peak Events change to match the
PSU Test Plan document.
•Added row detailing 80 Plus Silver Efficiency Levels in Table
4-16
•Added language and details in the table about Required
Efficiency levels are now part of how Low Load requirements
are defined in Section 4.5.8 and Table 4-17
•Added column for 10% Load as defined in ENERGY STAR* for
Computers v8 in Table 4-19
•Changed how 12VHPWR connector power limit labeling can be
done. Change from “Required” to “Recommended” for having
the 12VHPWR connector power limit on the 12VHPWR
connector. Reason is if a PSU uses a modular designs with
detachable cables, then the 12VHPWR power limit can be
listed on PSU Label. 12VHPWR connector limit must be listed
in one of these locations in Section 5.1
January
2023

10 613768
Document
Number
Revision
Number Description Revision Date
•Added mention of two options for 12VHPWR Connector,
header changed to “Recommended” for PSUs> 450 watts in
Section 5.2.2.4.3 -
•Updated Figure 5-4 and Figure 5-5 - figures with new pictures
of both 12VHPWR connector options
•Added paragraph & figure about 12VHPWR Cable Plug
Connection Recommendations in Section 5.2.2.4.3 and Figure
5-5
§§

Introduction
613768 11
1Introduction
This document aligns to ATX12VO Specification Version 2.0
This document provides design requirements for an industry standard focused on
single rail power supplies that will meet the existing mechanical size for power
supplies while providing the opportunity for higher platform power efficiency. Multi-rail
power supply designs have existed for many decades but as computers are evolving a
new single main power rail input power is needed to increase efficiency of the power
supply.
These single rail power supplies are primarily intended for use with desktop system
designs. The key parameters that define mechanical fit across a common set of
platforms does not change with existing power supply designs.
This Single Rail Power Supply Design Guide is intended to work for a majority of
desktop computer designs. The multi-rail Intel Desktop Power Supply Design Guide
(Doc#336521), includes criteria for many different varieties of desktop computers.
This document only details what needs to be included in the Single Rail Power Supply
Industry standard. The REQUIRED sections are intended to be followed for all
systems. The RECOMMENDED sections could be modified based on system design.
Lastly, a few sections are labeled as OPTIONAL, which would not be intended for all
design but is helpful to some designs.
The specification name for this Power Supply Design is ATX12VO, which stands for
ATX 12V Only. If the mechanical size of the power supply is different from ATX, for
example SFX then it would be SFX12VO.
This document covers the design parameters for the Power Supply to meet the
ATX12VO Specification.
1.1 Power Supplies and Alternative Low Power Mode
Computers are continuing to change and introducing new power states. One of these
new power states is generically called an Alternative Low Power Mode (ALPM). Some
examples of Alternative Low Power Modes are Microsoft* Windows 10 Modern Standby
or Google* Chrome* Lucid Sleep. These low power states have created requirements
for power supplies. Below is a summary of these requirements as they are mentioned
throughout the document. All ALPM features are required in this Single Rail Desktop
Power Supply Design Guide.
•Section 4.2.4: Other Lower Power System Requirements
To help meet multiple world-wide Energy Regulations the +5VSB standby rail
must meet the following efficiency as shown in Table 4-5 which is measured
with the main outputs off (PS_ON# high state). These World-Wide Energy
Regulations and standards include: Blue Angel* system requirements, RAL-
UZ 78, US Presidential executive order 13221, ENERGY STAR*, ErP Lot 6
requirements (2010 and 2013 levels), and 2014 ErP Lot 3 requirements.
Additionally, if any Computers use an Alternative Low Power Mode (ALPM)
then the +5VSB standby efficiency has similar requirements as shown below.
Table 4-5 shows that ALPM requirements are at the 230 mA and 625 mA load
levels.

Introduction
12 613768
•Section 4.3:
Table 4-9 “Required” timing values of T1 and T3 support ALPM. Multi rail
power supply design guide has the Required T1 and T3 timing values as
recommended for ALPM.
•Section 4.2.2– PS_ON#
•Section 10.2:
The number of times a PSU toggles on and off is expected to increase.
•Section 4.3.2:
PSU response quickly to toggling of PS_ON# signal
1.2 System Power Telemetry Feature
When ATX12VO was designed one pin was reserved in the main 10 pin connector for a
Telemetry feature. This Telemetry feature is the ability of the power supply to report
the percentage of rated power being used by the system. The system components can
then react when the power supply rated power limit is reached or exceeded. This is
reported as a percentage because power supplies come in many different power
ratings and there is no way for the power supply to tell the system its rated power
limit. The percentage method allows for a consistent method of telemetry between all
ATX12VO power supplies and the system.
The electrical details are explained further in Section 4.3.7.
1.3 References
The following documents are referenced in various sections of this design guide. For
guidelines not specifically mentioned here, refer to the appropriate document.
Document Description Document
Number/Source
IEEE Guide on the Surge Environment in Low-Voltage (1000 V and
Less) AC Power Circuits ANSI C62.41.1-2002
IEEE Guide on Surge Testing for Equipment Connected to Low-
Voltage AC Power Circuits ANSI C62.45-2002
European Association of Consumer Electronics Manufacturers
(EACEM*)
Hazardous Substance List / Certification
AB13-94-146
American National Standard for Methods of Measurement of Radio-
Noise Emissions from Low-Voltage Electrical and Electronic Equipment
in the Range of 9 kHz to 40 GHz for EMI testing
ANSI C63.4-2014

Introduction
613768 13
Document Description Document
Number/Source
IEC/UL/CSA 62368-1
IEC/UL/CSA 60950-1
EN 60950-1
EU Low Voltage Directive (2014/35/EU)
GB-4943 (China)
CNS 14336 (Taiwan BSMI)
CISPR32/EN55032 (Electromagnetic compatibility of multimedia
equipment - Emission requirements)
EU EMC Directive (2014/30/EU)
CISPR35/EN55035 (Electromagnetic compatibility multimedia
equipment Immunity requirements)
FCC Part 15 Class B (Radiated and Conducted Emissions)
PCI Express Card Electromechanical Specification Revision 5.0 PCISIG.com Doc # 15904
PCI Express Card Electromechanical (CEM) Engineering Change Notice
(ECN) – “Power Excursion Limits for 300-600w PCIe AICs”
PCISIG.com Doc # 16495
PCI Express Card Electromechanical (CEM) Engineering Change
Request (ECR) – “Power Excursion Limits for up to 300 W PCIe AICs”
PCISIG.com Doc # 16680
ENERGY STAR for Computers Version 8.0 https://www.energystar.g
ov/products/spec/compute
rs_version_8_0_pd
European Union Energy Related Products (ErP) Lot 6 https://ec.europa.eu/ener
gy/en/topics/energy-
efficiency/energy-efficient-
products/standby
Power Supply Efficiency Labeling Program – 80 plus Organization 80plus.org
Generalized Test Protocol for Calculating the Energy Efficiency of
Internal Ac-Dc and Dc-Dc Power Supplies Revision 6.7.1
EPRI – Listed at
80plus.org website
Efficiency (ETA) and Noise (LAMBDA) programs: Cybenetics LTD Cybenetics.com
1.4 Terminology
The below table defines the acronyms, conventions, and terminology that is used
throughout the design guide.

Introduction
14 613768
Table 1-1: Conventions and Terminology
Acronym/Convention/
Terminology Description
ALPM
Alternative Low Power Mode (ALPM) replaces the traditional Sleep
Mode (ACPI S3) and sometime Long Idle [Idle (S0) Display off]
with a new lower power mode. An example of ALPM is Microsoft*
Modern Standby* or Lucid Sleep with Google* Chrome*
AWG American Wire Gauge
BA
Declared sound power, LwAd. The declared sound power level
shall be measured according to ISO* 7779 for the power supply
and reported according to ISO 9296.
CFM Cubic Feet per Minute (airflow).
Monotonically A waveform changes from one level to another in a steady
fashion, without oscillation.
MTBF Mean time between failure.
Noise The periodic or random signals over frequency band of 0 Hz to 20
MHz.
Non-ALPM Computers that do not use Alternative Low Power Mode use
traditional Sleep Mode (ACPI S3).
Overcurrent
A condition in which a supply attempts to provide more output
current than the amount for which it is rated. This commonly
occurs if there is a "short circuit" condition in the load attached to
the supply.
PFC Power Factor Correction.
p-p Peak to Peak Voltage Measurement.
PWR_OK
PWR_OK is a “power good” signal used by the system power
supply to indicate that the +12VDC outputs are above the under-
voltage thresholds of the power supply.
Ripple noise The periodic or random signals over a frequency band of 0 Hz to
20 MHz.
Rise Time Rise time is defined as the time it takes any output voltage to rise
from 10% to 90% of its nominal voltage.
SELV
Safety Extra Low Voltage - UL 60950-1 states that a SELV circuit
is a “secondary circuit, which is so designed and protected that
under normal and single fault conditions, its voltages do not
exceed a safe value.” A “secondary circuit” has no direct
connection to the primary power (AC mains) and derives its
power via a transformer, converter, or equivalent isolation device
Surge The condition where the AC line voltage rises above nominal
voltage.
VSB or Standby Voltage An output voltage that is present whenever AC power is applied
to the AC inputs of the supply.

Introduction
613768 15
Table 1-2: Support Terminology
Category Description
Optional
The status given to items within this design guide, which are not required to
meet design guide, however, some system applications may optionally use
these features. May be a required or recommended item in a future design
guide.
Recommended
The status given to items within this design guide, which are not required to
meet design guide, however, are required by many system applications. May
be a required item in a future design guide.
Required The status given to items within this design guide, which are required to
meet design guide and a large majority of system applications.
§§

Processor Configurations
16 613768
2Processor Configurations
2.1 Processor Configurations (Recommended)
The processor power in a desktop computer is provided by the 12V2 power rail of
power supplies with multiple power rails. To meet the desktop processor power needs
a desktop power supply must provide the current value list in Table 2-1 for the 12V2
voltage rail. Table 2-1 shows the various processor current requirements represented
by the desktop processor’s TDP. If a power supply only has one 12V rail, then Table
2-1 shows the amount of current that needs to be dedicated to the desktop processor
in a system level power budget.
Table 2-1: Processor Configurations – 12V2 Current
PSU 12V2
Capability Recommendations
Processor TDP Continuous Current Peak Current
150 W 33 A 60 A
125 W 26 A 39 A
65 W 23 A 34 A
35 W 11 A 19 A
NOTES:
If the power supply supports the 240VA Energy Hazard protection requirement, then
current levels for the 12 Volt rail above 18 Amps would have to be split into multiple
12V rails.
Continuous current is defined for the processors PL2 (Turbo) power limit since desktop
processors are expected to stay at PL2 for many seconds, sometimes close to 1 minute.
For a PSU any time over 1 second is considered Continuous current.
Peak Current is defined for the processor’s PL4 which defines Peak current for a max
time of 10 ms.
All future processor power/PSU current requirements will be defined in a document
titled ATX12VO and ATX12V PSU Design Guide Addendum (# 621484) that is
applicable to both Single Rail and Multi Rail ATX Power Supplies. Refer to that
document for details of where these values come from.
2.2 High End Desktop Market Processor
Considerations
The High-End Desktop market requires power supplies with higher power levels than
typical mainstream market. The EPS12V specification is often referenced for these
designs. The EPS12V specification is a power supply form factor for the server market.
This Desktop ATX12VO Single Rail Power Supply design guide includes higher power
levels to support these higher performance desktop computers.

Processor Configurations
613768 17
2.2.1 Modular Power Supply Connectors
A modular power supply, with multiple detachable cable options is recommended to
provide the greatest flexibility to the end user. This approach reduces the chassis
volume consumed by unused power cables to improve cable routing and cooling.
The dedicated 12V CPU connectors on the motherboard are either a single 8 pin (2x4)
connector, or one or two 4 pin (2x2) connectors, detailed in Section 5.2.2.3 +12V CPU
Power Connector (Required). These are often referenced as EPS12V connectors.
Section 5.2.2.4 PCI-Express (PCIe*) Add-in Card Connector details three
cable/connector options to deliver +12 V power rails to a PCIe* Add-in Card. While
each of the three connectors provides a 12V rail to power the chassis component, they
use different pin locations and mechanical keying, and are not directly
interchangeable. Therefore, a modular design is an option to support multiple end use
configurations.
For example, the end user might require a power supply to support a system with a
lower-power or non-overclocked CPU and multiple higher-power graphics cards and
thus populate the PSU outputs with multiple power cables configured for the PCIe*
graphics cards. Alternatively, a higher power overclocked CPU system mounting a
single, lower power graphics card may require more 12V CPU power and a single plug
for PCIe* power. A modular power supply allows connectors on the power supply to
provide 12V power and then the end user can select the appropriately configured
cable/plug to provide 12V power in their system with no change to the pinout of the
PSU itself.
Here are some examples modular designs. The orange box in each picture identifies
where the connectors on the power supply are that provide 12V power rails.
18 AWG wire is typically used to meet the 6-8 Amp/pin requirements of most chassis
components. (Example of an exception to this it the 12VHPWR connector that uses
16AWG wires.) Based on this example of 6-8 Amp/pin the following recommendation
applies to how much power/current can be supported by each connector determined
by the number of +12V pins included in that connector. Using Table 2-1, the number
of pins and connectors for motherboard 12V CPU (EPS12V) connectors can be
calculated.
•12-16 A support for 2x2 (4pin) connector
•18-24 A support for 2x3 (6pin) connector
•24-32 A support for 2x4 (8pin) connector
A distinction must be made between the current per pin available at the PSU through
a connector pin and 18 AWG wire vs. the maximum demand for current from the
connected chassis component such as a PCIe* Card or motherboard 12V CPU
connector(s).

Processor Configurations
18 613768
For example, a standard 2x3 PCIe* power connector supporting a graphics card will
draw no more than 6.75 Amps total through its three power pins and two ground pins.
Similarly, the 2x4 PCIe* power connector will draw no more than 13.5 Amps total
through three power pins and three ground pins.
It is possible to reduce the number of conductors consumed at the PSU by providing
the 12V to a 2x4 PCIe* card power connector through a 2x2 modular connector at the
power supply, for example. Before reducing the conductor count, the PSU designer
should also consider the copper losses and the resulting voltage drop incurred by the
two cable connectors and a length of the 18 AWG conductor.
This recommendation is based on common design practice. The PSU and system
designer may deviate from this guidance but remains responsible for designing the
PSU to meet all electrical, thermal, safety and reliability requirements based on the
application of the PSU.
It is important to recognize that the new 600W 12VHPWR cable/plug introduced with
PCIe* Gen 5.0 (detailed in Section 5.2.2.4.3), requires 16 AWG wire and a per-pin
current capacity of 9.2 A.
2.2.2 Overclocking Recommendations
The power levels listed in Section 2.1 - Processor Configurations - RECOMMENDED are
for processors that follow the Plan of Record (POR) power levels that include Turbo
Mode. If the processor is overclocked, then power requirements will be increased. If
the power supply is expected to support end users who intend to overclock then the
12V power rail to the processor should be higher than what is listed in Table 2-1:
Processor Configurations.
§§

PCI Express* Add-in Card Considerations
613768 19
3PCI Express* Add-in Card
Considerations
The PCI Express* (PCIe*) Card Electromechanical Specification (CEM Spec) provides
thermal, power, mechanical, and signal integrity design guidance for the PCI Express*
Add-in Card (AIC) form factor. This includes the card’s electrical and mechanical
interface with a host system board, chassis, and power supply.
The 5.0 Revision of the PCIe* spec introduces four significant updates that directly
affect this power supply specification:
1. A Power Excursion allowance was introduced to support brief, high current
demands on power, beyond the rated TDP.
2. The maximum power consumption for a single Add-in Card was doubled to 600W.
This is the per-card limit from all sources combined.
3. A new 48V (nominal) power rail was added.
4. Two new Auxiliary Power Connectors were introduced to provide the full 600W on
a single cable connector. The new 12VHPWR connector supports 600W on the 12V
rail while the 48VHPWR provides 600W on the 48V rail. Four new sideband signal
conductors permit simple signaling between the Add-in Card and power supply.
3.1 PCIe* Add-in Card Power Excursions
PCI Express* CEM specifications prior to Revision 5.0 did not provide any allowance to
permit an Add-in Card to exceed the TDP power for its designated power range. This
effectively limited the absolute power consumption of each Add-in Card to a hard limit
such as 10 W, 75 W, 150 W, 225 W, or 300 W, even when it would be advantageous
for it to make short-duration high-current demands on a power rail.
It is recognized that while many existing PCIe* CEM products already exceed the card
power limits, in violation of prior PCIe* CEM specs, their power supplies were never
explicitly designed to withstand these excursions. Consequently, power excursions
beyond these limits, however brief, might cause unexpected card or system
malfunctions, potentially triggering PSU overcurrent protection (OCP) or voltage
droop. This risk increases when multiple PCIe* cards are installed in a system.
The PCIe* CEM 5.0 spec addresses the need for occasional power excursions by
permitting the card to briefly exceed the existing limits on supply power while still
abiding by the power limits on a time-averaged basis. This allows the power supply
and Add-in Card to jointly withstand increased power demands with a limited duration
and magnitude.
The PCIe* CEM 5.0 specification introduces the concept of Sustained Power, the
average power delivered though a single power cable in a 1-second moving interval.
This allows the card and power supply to operate within existing power and thermal
envelopes, since the excursions’ durations are very short and do not measurably
increase the average temperature of any component.
These updates are described in an Engineering Change Notice (ECN) to the PCI
Express* Card Electromechanical (CEM) Specification, Revision 5.0, and will be

PCI Express* Add-in Card Considerations
20 613768
integrated into the specification itself in upcoming releases. This ECN is titled “Power
Excursion Limits for 300W-600W PCIe* AICs” (Doc# 16495). This ECN defines power
excursions, which are a “temporary condition in which the power exceeds the
maximum sustained power”. The ECN states the purpose of the document is to “allow
system designers to properly design power subsystems to enable these excursions”.
Based on this PCIe* ECN, this section of the ATX Power Supply Design Guide will
provide guidance for power supplies to be designed to meet the permitted power
excursions of PCIe* Add-in Cards.
Note that Add-in Cards with power from 300-600 watts did not exist prior to the PCIe*
CEM 5.0 specification. Earlier generations of PCIe* Add-in Cards were limited to 300
Watts or below. While many of the relevant specification updates are duplicated here
for convenience, designers should confirm that they have the most up to date
information by consulting the reference documentation on https://www.pcisig.com.
The information below is drawn from the PCIe* documentation at the time of
publication of this document.
The power consumption excursions allowed in a PCIe* Add-in Card rated at 300 watts
to 600 watts, only when the mount one of new 12VHPWR or 48VHPWR power
connectors, also introduced in PCIe* CEM 5.0. The 48VHPWR connector is not relevant
to this document and therefore will not be discussed further. Similar power excursions
are not permitted for the legacy 2x3 and 2x4 PCIe* Auxiliary Power connectors since
that would introduce backward compatibility risks with legacy power supplies.
A second Engineering Change Request, “Power Excursion Limits up to 300 Watts” is
under consideration. This ECR would define similar power excursions for the 12VHPWR
Auxiliary Power connector for cards less than 300 Watts. It is likely that an identical
Power Excursion allowance will be adopted for Add-in Cards rated at 300 W or less, so
power supply vendors are advised to provision any 12V rails supporting the 12VHPWR
connector with support for Power Excursions at all power levels.
The power supply must be able to provide voltages that remain within the
requirements defined in Table 4-2 (Section 4.2) during the defined power excursions.
Add-in Card power consumption excursion limits are defined by the maximum ratio
(R) of average power consumption in any continuous time interval (T) relative to the
maximum sustained (average) power of that Add-in Card.
At all times, the Add-in Card must concurrently adhere to the power excursion limits
for all time interval lengths as defined in Table 3-1 and Figure 3-1 as well as the
rolling time average of the sustained power of the card.Table 3-1 shows the power
excursion limits for all time intervals in which “R” is calculated by dividing the average
power consumption in a continuous time interval of length “T” but the maximum
sustained power of that Add-in Card. The Add-in Card must also stay within all voltage
tolerance and current as defined in Section 3.2 and Table 3-5.
Table 3-1: PCI Express CEM Add-in Card Power Excursion Limits Table45
Average Power Calculation
Interval Length in
microseconds(µs)
“T”
Ratio of Average Power1in
Interval “T” Divided by
Maximum Sustain Power
Notes
≤ 100 3 2
>100 and 4 – 0.2171 x ln(T) 3