Enhance ATX12V Version 1.1 Power Supply Design Guide
ATX / ATX12V Power Supply Design Guide
Version 1.1
ATX/ATX12V Power Supply Design Guide
Version 1.1
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Copyright 2000 Intel Corporation. All rights reserved.
Version 1.1
†
Third-party brands and names are the property of t hei r respective owners.
Revision History
Version Summary of Changes Date
1.0 Initial Release Feb. 2000
1.1 Increase 3.3 V current; add more explanation for power sharing; do minor edits and
format fixes
Aug. 2000
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ATX/ATX12V Power Supply Design Guide
Version 1.1
Contents
1. Introduction...................................................................................................... 6
1.1. Scope .................................................................................................................................... 6
1.2. New for ATX12V as Compared with ATX Power Supply....................................................... 6
1.2.1. ATX12V .................................................................................................................... 6
1.2.2. Increased +5 VSB Current........................................................................................ 7
2. Applicable Documents..................................................................................... 8
3. Electrical........................................................................................................... 9
3.1. AC Input................................................................................................................................. 9
3.1.1. Input Overcurrent Protection..................................................................................... 9
3.1.2. Inrush Current Limiting ............................................................................................. 9
3.1.3. Input Undervoltage....................................................................................................9
3.1.4. Immunity ................................................................................................................... 10
3.1.5. Catastrophic Failure Protection ................................................................................ 10
3.2. DC Output.............................................................................................................................. 10
3.2.1. DC Voltage Regulation ............................................................................................. 10
3.2.2. Remote Sensing ....................................................................................................... 11
3.2.3. Typical Power Distribution ........................................................................................ 11
3.2.4. Power Limit............................................................................................................... 14
3.2.5. Efficiency................................................................................................................... 14
3.2.6. Output Ripple/Noise.................................................................................................. 15
3.2.7. Output Transient Response...................................................................................... 16
3.2.8. Capacitive Load........................................................................................................ 16
3.2.9. Closed-loop Stability.................................................................................................16
3.2.10. +5 VDC / +3.3 VDC Power Sequencing ................................................................. 17
3.2.11. Voltage Hold-up Time............................................................................................. 17
3.3. Timing / Housekeeping / Control ........................................................................................... 17
3.3.1. PWR_OK .................................................................................................................. 17
3.3.2. PS_ON#.................................................................................................................... 18
3.3.3. +5 VSB...................................................................................................................... 19
3.3.4. Power-on Time .........................................................................................................19
3.3.5. Risetime.................................................................................................................... 19
3.3.6. Overshoot at Turn-on / Turn-off................................................................................ 20
3.3.7. Reset after Shutdown ............................................................................................... 20
3.3.8. +5 VSB at AC Power-down....................................................................................... 20
3.4. Output Protection................................................................................................................... 20
3.4.1. Overvoltage Protection ............................................................................................. 20
3.4.2. Short-circuit Protection ............................................................................................. 21
3.4.3. No-load Operation .................................................................................................... 21
3.4.4. Overcurrent Protection.............................................................................................. 21
3.4.5. Overtemperature Protection ..................................................................................... 21
3.4.6. Output Bypass .......................................................................................................... 21
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ATX/ATX12V Power Supply Design Guide
Version 1.1
4. Mechanical........................................................................................................ 22
4.1. Labeling / Marking ................................................................................................................. 22
4.2. Physical Dimensions ............................................................................................................. 22
4.3. Airflow / Fan........................................................................................................................... 25
4.4. AC Connector........................................................................................................................ 26
4.5. DC Connectors...................................................................................................................... 26
4.5.1. ATX Main Power Connector ..................................................................................... 27
4.5.2. +12 V Power Connector (for ATX12V Configurations Only)..................................... 28
4.5.3. Auxiliary Power Connector for Configurations with +3.3 VDC Output > 18 A
or +5 V Output > 24 A............................................................................................... 28
4.5.4. Peripheral Connector(s)............................................................................................ 28
4.5.5. Floppy Drive Connector............................................................................................ 28
5. Environmental.................................................................................................. 29
5.1. Temperature.......................................................................................................................... 29
5.2. Thermal Shock (Shipping)..................................................................................................... 29
5.3. Humidity................................................................................................................................. 29
5.4. Altitude................................................................................................................................... 29
5.5. Mechanical Shock ................................................................................................................. 29
5.6. Random Vibration.................................................................................................................. 30
5.7. Acoustics ............................................................................................................................... 30
6. Electromagnetic Compatibility........................................................................ 31
6.1. EMI ........................................................................................................................................ 31
6.2. Input Line Current Harmonic Content and Line Flicker Required for Sales
in Europe and Japan.............................................................................................................. 31
6.3. Magnetic Leakage Fields....................................................................................................... 31
7. Reliability.......................................................................................................... 32
7.1. Component Derating ............................................................................................................. 32
7.2. Mean Time Between Failures (MTBF) .................................................................................. 32
8. Safety ................................................................................................................ 33
8.1. North America........................................................................................................................ 33
8.2. International........................................................................................................................... 34
8.3. Proscribed Materials.............................................................................................................. 34
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ATX/ATX12V Power Supply Design Guide
Version 1.1
Figures
Figure 1. Differential Noise Test Setup................................................................................................. 15
Figure 2. Power Supply Timing............................................................................................................. 17
Figure 3. PS_ON# Signal Characteristics............................................................................................. 19
Figure 4. Power Supply Dimensions for Chassis in Which the P/S Does Not Cool Processor ............ 23
Figure 5. Power Supply Dimensions for Chassis in Which the P/S Cools the Processor..................... 24
Figure 6. ATX and ATX12V Power Supply Connectors........................................................................ 27
Tables
Table 1. Power Supply Feature Summary, ATX versus ATX12V......................................................... 7
Table 2. AC Input Line Requirements................................................................................................... 9
Table 3. DC Output Voltage Regulation................................................................................................ 10
Table 4. Typical Power Distribution for a 160 W ATX Configuration .................................................... 11
Table 5. Typical Power Distribution for a 200 W ATX Configuration .................................................... 12
Table 6. Typical Power Distribution for a 250 W ATX Configuration .................................................... 12
Table 7. Typical Power Distribution for a 300 W ATX Configuration .................................................... 12
Table 8. Typical Power Distribution for a 200 W ATX12V Configuration.............................................. 13
Table 9. Typical Power Distribution for a 250 W ATX12V Configuration.............................................. 13
Table 10. Typical Power Distribution for a 300 W ATX12V Configuration............................................ 14
Table 11. DC Output Noise/Ripple........................................................................................................ 15
Table 12. DC Output Transient Step Sizes........................................................................................... 16
Table 13. Output Capacitive Loads....................................................................................................... 16
Table 14. PWR_OK Signal Characteristics .......................................................................................... 18
Table 15. PS_ON# Signal Characteristics ............................................................................................ 18
Table 16. Overvoltage Protection.......................................................................................................... 20
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ATX/ATX12V Power Supply Design Guide
Version 1.1
1. Introduction
1.1. Scope
This document provides design suggestions and reference specifications for a family of
power supplies that comply with the ATX Specification, Version 2.03* for motherboards
and chassis. It includes supplementary information not expressly detailed in the ATX
Specification, such as information about the physical form factor of the power supply,
cooling requirements, connector configuration, and pertinent electrical and signal timing
specifications.
This document is provided as a convenience only and is not intended to replace the user’s
independent design and validation activity. It should not be inferred that all ATX or
ATX12V power supplies must conform exactly to the content of this document. Neither
are the design specifics described herein intended to support all possible system
configurations, because system power supply needs vary widely depending on factors such
as the application (that is, for desktop, workstation, or server), intended ambient
environment (temperature, line voltage), or motherboard power requirements.
1.2. New for ATX12V as Compared with ATX Power Supply
This section briefly summarizes the major changes made to this document that now
includes the ATX12V power supply. An earlier design guide covered only the ATX power
supply. There are also a few changes from Version 1.0 to 1.1 (increased 3.3 V current,
more explanation for power sharing).
1.2.1. ATX12V
A new superset of the original ATX power supply has been defined. Named “ATX12V,”
this new power supply is comprised of a standard ATX unit plus the following
enhancements:
• Increased +12 VDC output capability. Motherboard components with unique voltage
requirements are increasingly expected to be powered via DC/DC converters off the
+12 VDC power supply output. This trend is due primarily to the higher power
conversion and transmission efficiencies of +12 VDC relative to +5 VDC or +3.3 VDC.
ATX12V power supplies should be designed to accommodate these increased +12 VDC
current requirements and to address associated issues such as cross-regulation,
capacitive loading, transient surge tolerance, cable voltage drop, and cooling.
*
2.03 is the current version of the ATX Specification as of this writing. Future references to the ATX
Specification in this document imply version 2.03 or later, as applicab le.
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ATX/ATX12V Power Supply Design Guide
Version 1.1
• Power Connectors. To enable the delivery of more +12 VDC current to the
motherboard, a new 4-pin receptacle/header combination—the +12 V power
connector—has been defined. The presence of the +12 V power connector indicates
that a power supply is ATX12V; the absence of the +12 V power connector
indicates that a supply is ATX. To allow for greater than 3.3 V current, the Aux
Power Connector is recommended for ATX and ATX12V power supplies with 3.3 V
current > 18 A. See Sections 3.2.3.2 and 4.5 for details on the +12 V and AUX power
connector.
ATX12V power supplies are intended to be downward compatible with ATX power
supplies. Consequently, it is required that an ATX12V power supply be able to provide the
same typical +5 VDC and +3.3 VDC maximum continuous output currents as an ATX
supply of the same total output power. To minimize cost, this may be accomplished via a
load sharing arrangement, whereby the individual +12 VDC, +5 VDC, and +3.3 VDC
output currents may trade off against each other but the combined total output power is
constrained to not exceed a limit specified by the power supply designer. Such an approach
can effectively support both +5 VDC- or +12 VDC-centric motherboards.
The standard ATX power supply definition will be maintained in parallel with ATX12V—
despite the downward compatibility of ATX12V—because both offer distinct advantages to
the industry:
• An ATX power supply supports motherboards that rely on DC/DC conversion from
+5 VDC or +3.3 VDC only. This limitation and an initial volume advantage make it
more attractive for focussed, cost-sensitive system platforms.
• An ATX12V power supply supports motherboards that rely on DC/DC conversion from
either +12 VDC, +5 VDC, or +3.3 VDC, yielding more application flexibility for future
platforms.
1.2.2. Increased +5 VSB Current
Trends in PC system power management solutions (for example, “Instantly Available PC,”
“Suspend-to-RAM”) are driving a need for increased +5 VSB current capability for all
ATX-family power supplies. The previous +5 VSB output requirement is being raised to
1.0 amps minimum, with 2.0 amps preferred. Recommendations for momentary peak
current have also been added to enable USB "wake on" devices. See Section 3.3.3 for
details.
Table 1. Power Supply Feature Summary,
ATX versus ATX12V
ATX ATX12V
+12 V power connector No Yes
+5 VSB current 1.0 amps 1.5 Peak (required)
2.0 amps 2.5 Peak (recommended)
1.0 amps 1.5 Peak (required)
2.0 amps 2.5 Peak (recommended)
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ATX/ATX12V Power Supply Design Guide
Version 1.1
2. Applicable Documents
The latest revision in effect of the following documents forms a part of this document to the
extent specified.
Document title Description
AB13-94-146
ANSI C62.41-1991 IEEE Recommended Practice on Surge Voltages in Low-Voltage AC Circuits
ANSI C62.45-1992 IEEE Guide on Surge Testing for Equipment Connected to Low-Voltage AC Power
MIL-STD-105K Quality Control
MIL-STD-217F Reliability Predictions for Electronic Equipment
MIL-C-5541 Chemical Conversion Coatings on Aluminum and Aluminum Alloys
CSA C22.2 No.234, Level 3 Safety of Component Power Supplies (Intended for use with Electronic Data
CAN/CSA C22.2 No.950-95,
rd
edition
3
UL 1950, 3rd edition, without D3
Deviation
IEC 60950 plus A1, A2, A3, A4 Safety of Information Technology Equipment Including Business Equipment
EN 60950 plus A1, A2, A3, A4 Safety of Information Technology Equipment Including Business Equipment
EMKO-TSE (74-SEC) 207/94 Nordic national requirement in addition to EN 60950
CISPR 22:1997 3rd edition
EN 55022:1998
ANSI C63.4 – 1992 American National Standard for Methods of Measurement of Radio-Noise
EN 55024:1998 Information technology equipment—Immunity characteristics—Limits and methods
EN 61000-3-2 Electromagnetic compatibility (EMC)—Part 3: Limits—Section 2: Limits for
IEC 61000-4- Electromagnetic compatibility (EMC) for industrial-process measurement and
Japan Electric Association Guidelines for the Suppression of Harmonics in Appliances and General Use
IEC Publication 417 International Graphic Symbol Standard
ISO Standard 7000 Graphic Symbols for Use on Equipment
CFR 47, Part 15, Subpart B FCC Rules
European Association of Consumer Electronics Manufacturers (EACEM)
Hazardous Substance List / Certification
Circuits
Processing Equipment and Office Machines)
Safety of Information Technology Equipment Including Electrical Business
Equipment
Safety of Information Technology Equipment Including Electrical Business
Equipment
Limits and Methods of Measurements of Radio Interference Characteristics of
Information Technology Equipment, Class B
Emissions from Low-Voltage Electrical and Electronic Equipment in the Range of 9
kHz to 40 GHz for EMI testing
of measurement
harmonic current emissions, Class D
control equipment—Part 4: Testing and measurement techniques
Section -2: Electrostatic discharge
Section -3: Radiated, radio-frequency, electromagnetic field
Section -4: Electrical fast transient / burst
Section -5: Surge
Section -6: Conducted disturbances, induced by radio-frequency fields
Section -8: Power frequency magnetic fields
Section -11: Voltage dips, short interruptions, and voltage variations
Equipment
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ATX/ATX12V Power Supply Design Guide
3. Electrical
The electrical requirements that follow are to be met over the environmental ranges
specified in Section 5 unless otherwise noted.
3.1. AC Input
Table 2 lists AC input voltage and frequency requirements for continuous operation. The
power supply shall be capable of supplying full-rated output power over two input voltage
ranges rated 100-127 VAC and 200-240 VAC rms nominal. The correct input range for
use in a given environment may be either switch-selectable or autoranging. The power
supply shall automatically recover from AC power loss. The power supply must be able to
start up under peak loading at 90 VAC.
Table 2. AC Input Line Requirements
Parameter Min. Nom.
(1)
Max. Unit
Version 1.1
Vin (115 VAC) 90 115 135 VAC
Vin (230 VAC) 180 230 265 VAC
Vin Frequency 47 -- 63 Hz
(1)
Nominal voltages for test purposes are considered to be within ±1.0 V of nominal.
rms
rms
3.1.1. Input Overcurrent Protection
The power supply shall incorporate primary fusing for input overcurrent protection to
prevent damage to the power supply and meet product safety requirements. Fuses should
be slow-blow–type or equivalent to prevent nuisance trips.
3.1.2. Inrush Current Limiting
Maximum inrush current from power-on (with power on at any point on the AC sine) and
including, but not limited to, three line cycles, shall be limited to a level below the surge
rating of the input line cord, AC switch if present, bridge rectifier, fuse, and EMI filter
components. Repetitive ON/OFF cycling of the AC input voltage should not damage the
power supply or cause the input fuse to blow.
3.1.3. Input Undervoltage
The power supply shall contain protection circuitry such that the application of an input
voltage below the minimum specified in Section 3.1, Table 2, shall not cause damage to the
power supply.
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ATX/ATX12V Power Supply Design Guide
Version 1.1
3.1.4. Immunity
At a minimum, a system and power supply typically must pass testing per the limits and
methods described in EN 55024 prior to sale in many parts of the world. Additional
requirements may depend on the design, product end use, target geography, customer, and
other variables. Consult your company’s Product Safety and Regulations department for
more details.
3.1.5. Catastrophic Failure Protecti on
Should a component failure occur, the power supply should not exhibit any of the
following:
• Flame
• Excessive smoke
• Charred PCB
• Fused PCB conductor
• Startling noise
• Emission of molten material
3.2. DC Output
3.2.1. DC Voltage Regulation
The DC output voltages shall remain within the regulation ranges shown in Table 3 when
measured at the load end of the output connectors under all line, load, and environmental
conditions. The voltage regulation limits shall be maintained under continuous operation
for a period of time equal to or greater than the MTBF specified in Section 7.2 at any steady
state temperature and operating conditions specified in Section 5.
Table 3. DC Output Voltage Regulation
Output Range Min. Nom. Max. Unit
+12VDC
+5VDC ±5% +4.75 +5.00 +5.25 Volts
+3.3VDC ±5% +3.14 +3.30 +3.47 Volts
-5VDC ±10% -4.50 -5.00 -5.50 Volts
-12VDC ±10% -10.80 -12.00 -13.20 Volts
+5VSB ±5% +4.75 +5.00 +5.25 Volts
(1)
(1)
At +12 VDC peak loading, regulation at the +12 VDC output can go to ± 10%.
±5% +11.40 +12.00 +12.60 Volts
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ATX/ATX12V Power Supply Design Guide
3.2.2. Remote Sensing
The +3.3 VDC output should have provisions for remote sensing to compensate for
excessive cable drops. The default sense should be connected to pin 11 of the main power
connector. The power supply should draw no more than 10 mA through the remote sense
line to keep DC offset voltages to a minimum.
3.2.3. Typical Power Distribution
DC output power requirements and distributions will vary widely based on specific system
options and implementation. Significant dependencies include the quantity and types of
processors, memory, add-in card slots, and peripheral bays, as well as support for advanced
graphics or other features. It is ultimately the responsibility of the designer to derive a
power budget for a given target product and market.
Tables 4 through 10 provide sample power distributions and cross-loading diagrams as a
reference only. The tabular data summarizes maximum and minimum loadings on each
output, regardless of cross-regulation. The diagrams show typical assumptions for crossloading: The area within each plotted perimeter represents the power usage of a
motherboard and system platform. At a minimum, the power supply must have the
capability to provide power for the area inside the plotted area. The power supply may
provide additional margin for the area outside the perimeter. In each graph, the vertical line
on the right side shows the recomended combined power from 3.3 V and 5 V; the upper
horizontal line is the recommended 12 V power; and the total power is the power expected
from all rails for any system configuration. The power supply will share power between the
5 V, 3.3 V, and 12 V to provide the maximum rated power under the possible loading
conditions shown in each graph. It should not be inferred that all power supplies must
conform to these tables, nor that a power supply designed to meet the information in the
tables will work in all system configurations.
Version 1.1
3.2.3.1. ATX Configurations Table 4. Typical Power Distribution for a 160 W ATX Configuration
Min.
Current
Output
+12 VDC 0.0 6.0 8.0
+5 VDC 1.0 18.0
+3.3 VDC 0.3 14.0
-5 VDC 0.0 0.3
-12 VDC 0.0 0.8
+5 VSB 0.0 1.5 2.5
(amps)
Max.
Current
(amps)
See graph at right for power sharing.
Peak
Current
(amps)
80
70
60
50
40
30
+12V load (W)
20
10
0
0 20 40 60 80 100 120
+5V & +3.3V co m b ined lo ad (W)
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