Intel ATX12V User Manual
ATX12V Power Supply Design Guide
Version 2.0
ATX12V Power Supply Design Guide
Version 2.0
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ATX12V Power Supply Design Guide
Version 2.0
Contents
1. Introduction ....................................................................................................... 6
1.1. Scope .....................................................................................................................................6
1.2. Key Changes for ATX12V Version 2.0 as Compared with ATX Power Supply......................6
1.2.1. Increased +12 VDC output capability ........................................................................6
1.2.2. Minimum Efficiency....................................................................................................6
1.2.3. Main Power Connector: .............................................................................................7
1.2.4. Separate current limit for 12V2 on the 2x2 connector: ...............................................7
1.3 Terminology.............................................................................................................................7
2. Applicable Documents ..................................................................................... 8
3. Electrical ............................................................................................................ 9
3.1. AC Input..................................................................................................................................9
3.1.1. Input Over-current Protection ....................................................................................9
3.1.2. Inrush Current Limiting ..............................................................................................9
3.1.3. Input Under-voltage ...................................................................................................10
3.1.4. Regulatory..................................................................................................................10
3.1.5. Catastrophic Failure Protection .................................................................................11
3.2. DC Output...............................................................................................................................11
3.2.1. DC Voltage Regulation ..............................................................................................11
3.2.2. Remote Sensing ........................................................................................................12
3.2.3. Typical Power Distribution .........................................................................................12
3.2.4. Power Limit / Hazardous Energy Levels....................................................................17
3.2.5. Efficiency ...................................................................................................................17
3.2.6. Output Ripple/Noise...................................................................................................19
3.2.7. Output Transient Response.......................................................................................21
3.2.8. Capacitive Load .........................................................................................................21
3.2.9. Closed-loop Stability ..................................................................................................22
3.2.10. +5 VDC / +3.3 VDC Power Sequencing ..................................................................22
3.2.11. Voltage Hold-up Time ..............................................................................................22
3.3. Timing / Housekeeping / Control ............................................................................................22
3.3.1. PWR_OK ...................................................................................................................23
3.3.2. PS_ON#.....................................................................................................................23
3.3.3. +5 VSB.......................................................................................................................24
3.3.4. Power-on Time ..........................................................................................................25
3.3.5. Risetime.....................................................................................................................25
3.3.6. Overshoot at Turn-on / Turn-off.................................................................................25
3.3.7. Reset after Shutdown ................................................................................................25
3.3.8. +5 VSB at AC Power-down........................................................................................25
3.4. Output Protection....................................................................................................................26
3.4.1. Over-voltage Protection .............................................................................................26
3.4.2. Short-circuit Protection ..............................................................................................26
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ATX12V Power Supply Design Guide
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3.4.3. No-load Operation .....................................................................................................26
3.4.4. Over-current Protection .............................................................................................26
3.4.5. Over-temperature Protection .....................................................................................27
3.4.6. Output Bypass ...........................................................................................................27
4. Mechanical......................................................................................................... 28
4.1. Labeling / Marking ..................................................................................................................28
4.2. Physical Dimensions ..............................................................................................................28
4.3. Airflow / Fan............................................................................................................................31
4.4. AC Connector .........................................................................................................................32
4.5. DC Connectors .......................................................................................................................32
4.5.1. ATX Main Power Connector ......................................................................................34
4.5.2. +12 V Power Connector.............................................................................................35
4.5.3. Peripheral Connector(s).............................................................................................35
4.5.4. Serial ATA Power Connector.....................................................................................36
4.5.5. Floppy Drive Connector .............................................................................................36
5. Environmental ................................................................................................... 37
5.1. Temperature ...........................................................................................................................37
5.2. Thermal Shock (Shipping)......................................................................................................37
5.3. Humidity..................................................................................................................................37
5.4. Altitude....................................................................................................................................37
5.5. Mechanical Shock ..................................................................................................................38
5.6. Random Vibration...................................................................................................................38
5.7. Acoustics ................................................................................................................................38
6. Electromagnetic Compatibility......................................................................... 39
6.1. Emissions ...............................................................................................................................39
6.2. Immunity ...................................................................................................................................39
6.3. Input Line Current Harmonic Content and Line Flicker ..........................................................40
6.4. Magnetic Leakage Fields........................................................................................................40
7. Reliability ........................................................................................................... 41
7.1. Component De-rating .............................................................................................................41
8. Safety ................................................................................................................. 42
8.1. North America ........................................................................................................................42
8.2. International............................................................................................................................43
8.3. Proscribed Materials...............................................................................................................43
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ATX12V Power Supply Design Guide
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Figures
Figure 1. Cross Loading Graph for 250W Configuration .......................................................................13
Figure 2. Cross Loading Graph for 300W Configuration .......................................................................14
Figure 3. Cross Loading Graph for 350W Configuration .......................................................................15
Figure 4. Cross Loading Graph for 400W Configuration .......................................................................16
Figure 5. Differential Noise Test Setup .................................................................................................20
Figure 6. Power Supply Timing .............................................................................................................22
Figure 7. PS_ON# Signal Characteristics .............................................................................................24
Figure 8. Power Supply Dimensions for Chassis That Does Not Require Top Venting .......................29
Figure 9. Power Supply Dimensions for Chassis That Require Top Venting........................................30
Figure 10. ATX12V Power Supply Connectors .....................................................................................33
Figure 11. Serial ATA Connector ...........................................................................................................36
Tables
Table 1. AC Input Line Requirements ...................................................................................................9
Table 2. DC Output Voltage Regulation................................................................................................11
Table 3. Typical Power Distribution for a 250 W ATX12V Configuration..............................................13
Table 4. Typical Power Distribution for a 300 W ATX12V Configuration..............................................14
Table 5. Typical Power Distribution for a 350 W ATX12V Configuration..............................................15
Table 6. Typical Power Distribution for a 400 W ATX12V Configuration..............................................16
Table 7. Minimum Efficiency Vs Load...................................................................................................17
Table 8. Loading Table for Efficiency Measurements...........................................................................18
Table 9. Energy Star Input Power Consumption...................................................................................19
Table 10. DC Output Noise/Ripple........................................................................................................20
Table 11. DC Output Transient Step Sizes ...........................................................................................21
Table 12. Output Capacitive Loads.......................................................................................................21
Table 13. PWR_OK Signal Characteristics ..........................................................................................23
Table 14. PS_ON# Signal Characteristics ............................................................................................24
Table 15. Overvoltage Protection .........................................................................................................26
Table 16. Harmonic Limits, Class D Equipment ...................................................................................40
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ATX12V Power Supply Design Guide
Version 2.0
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
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 ATX12V
power supplies must conform exactly to the content of this document. The design specifics
described herein are not intended to support all possible system configurations. 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.
†
for motherboards
1.2. Key Changes for ATX12V Version 2.0 as Compared with ATX Power Supply
This section briefly summarizes the major changes made to this document that now defines
ATX12V power supply. With the move to 12V voltage regulators for the processor, ATX
guidelines for 5V as main power are no longer provided.
1.2.1. Increased +12 VDC output capability
System components that use 12V are continuing to increase in power. In cases where
expected current requirements is greater than 18A a second 12 V rail should be made
available. ATX12V power supplies should be designed to accommodate these increased
+12 VDC currents.
1.2.2. Minimum Efficiency
Minimum measured efficiency is required to be 70% at full and typical (~50%) load and
60% at light (~20%) load. New recommended guidance has been added to provide direction
for future requirements.
†
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
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, as applicable.
ATX12V Power Supply Design Guide
Version 2.0
1.2.3. Main Power Connector:
The 2 x 10 main power connector has been replaced by a 2 x 12 connector. This was made to
support 75 watt PCI Express*requirements. Pinout assignments are based on the SSI
recommendation.
With the added 12V, 5V, and 3.3V pins the need for an Aux Power connector is no longer
needed and the guidance for this connector has been removed.
1.2.4. Separate current limit for 12V2 on the 2x2 connector:
The 12V rail on the 2 x 2 power connector should be a separate current limited output to meet
the requirements of UL and EN 60950.
1.3 Terminology
The following terms are used in this document:
Term Description
Required
Recommended
Optional
BA
CFM
Monotonically
Noise
The status given to items within this design guide, which are required to meet
design guide and a large majority of system applications.
The status given to items within this design guide, which are not required to
meet design guide, however, are required by many system applications.
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.
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.
Cubic Feet per Minute (airflow).
A waveform changes from one level to another in a steady fashion, without
intermediate retracement or oscillation.
The periodic or random signals over frequency band of 0 Hz to 20 MHz.
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ATX12V Power Supply Design Guide
Version 2.0
2. Applicable Documents
The following documents support this design guide as additional reference material.
Document Title Description
FCC Rules Part 15, Class B Title 47, Code of Federal Regulations, Part 15
ICES-003: 1997, Class B Interference-Causing Equipment Standard – Digital Apparatus
EN 55022: 1998 +
Amendment A1:2000 Class B
CISPR 22: 1997, Class B
AS/NZS 3548:1995, Class B
EN 55024:1998
IEC 60950, 3rd ed., 1999 Safety of Information Technology Equipment
EN 60950: 2000 Safety of Information Technology Equipment
UL 60950, 3rd ed., 2000 Safety of Information Technology Equipment
CSA 22.2 No. 60950-00 Safety of Information Technology Equipment
Information Technology Equipment – Radio disturbance characteristics – Limits
and methods of measurement
Information Technology Equipment – Radio disturbance characteristics – Limits
and methods of measurement
Information Technology Equipment – Radio disturbance characteristics – Limits
and methods of measurement
Information Technology Equipment – Immunity Characteristics – Limits and
methods of measurement
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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 1 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 auto-ranging. 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 1. AC Input Line Requirements
Version 2.0
Parameter Minimum Nominal+ Maximum Unit
Vin (115 VAC) 90 115 135 VAC
Vin (230 VAC) 180 230 265 VAC
Vin Frequency 47 -- 63 Hz
+Note: Nominal voltages for test purposes are considered to be within ±1.0 V of nominal.
3.1.1. Input Over-current Protection
The power supply shall incorporate primary fusing for input over-current 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.
rms
rms
‡
. For Denmark and Switzerland international safety requirements, if the internal over-current protective
devices exceed 8A for Denmark and 10A for Switzerland, then the power supply must pass international
safety testing to EN 60950 using a maximum 16A over-current protected branch circuit, and this 16A (time
delay fuse) branch circuit protector must not open during power supply abnormal operation (output short
circuit and component fault) testing.
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ATX12V Power Supply Design Guide
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3.1.3. Input Under-voltage
The power supply shall contain protection circuitry such that the application of an input
voltage below the minimum specified in Section 3.1, Table 1, shall not cause damage to the
power supply.
3.1.4. Regulatory
The power supply is required to be tested and comply with the most current version
of the following regulatory specification requirements and/or standards
PRODUCT SAFETY
UL* 60950, 3
EN*60 950, 3
IEC*60 950, 3rd Edition (CB Report to include all national deviations)
EU* Low Voltage Directive (73/23/EEC) (CE Compliance)
rd
Edition –CAN/CSA-C22.2-60950-00,
rd
Edition
GB4943-90 CCIB* (China)
ELECTROMAGNETIC CAMPATIBILITY
FCC*, Class B, Part 15 (Radiated & Conducted Emissions)
CISPR* 22 / EN55022, 3rd Edition (Radiated & Conducted Emissions)
EN55024 (ITE Specific Immunity)
EN 61000-4-2 – Electrostatic Discharge
EN 61000-4-3– Radiated RFI Immunity
EN 61000-4-4– Electrical Fast Transients.
EN 61000-4-5 – Electrical Surge
EN 61000-4-6 – RF Conducted
EN 61000-4-8 – Power Frequency Magnetic Fields
EN 61000-4-11 – Voltage Dips, Short Interrupts and Fluctuations
EN61000-3-2 (Harmonics)
EN61000-3-3 (Voltage Flicker)
EU EMC Directive ((8/9/336/EEC) (CE Compliance)
Other Certifications and/or Declarations
GB925 (China/CCC*), CNS13438 (Taiwan/BSMI*),
AS/NZ3548 (Australia/C-tick* based on CISPR22)
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ATX12V Power Supply Design Guide
3.1.5. Catastrophic Failure Protection
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
Version 2.0
3.2.1. DC Voltage Regulation
The DC output voltages shall remain within the regulation ranges shown in Table 2 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 any steady state temperature and operating conditions specified in Section 5.
Table 2. DC Output Voltage Regulation
Output Range Min. Nom. Max. Unit
+12V1DC ±5% +11.40 +12.00 +12.60 Volts
+12V2DC
+5VDC ±5% +4.75 +5.00 +5.25 Volts
+3.3VDC
-12VDC ±10% -10.80 -12.00 -13.20 Volts
+5VSB ±5% +4.75 +5.00 +5.25 Volts
(1)
At +12 VDC peak loading, regulation at the +12 VDC output can go to ± 10%.
(2)
Voltage tolerance is required at main connector and S-ATA connector (if used).
(1)
±5% +11.40 +12.00 +12.60 Volts
(2)
±5% +3.14 +3.30 +3.47 Volts
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ATX12V Power Supply Design Guide
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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 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.
Table 3 through Table 5 and Figure 1 through Figure 3 provide sample power distributions
and a graphical recommendation for cross loading. 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.
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ATX12V Power Supply Design Guide
3.2.3.1. ATX12V Configurations
Table 3. Typical Power Distribution for a 250 W ATX12V Configuration
Output
+12 V1DC
+12 V2DC
+5 VDC
+3.3 VDC
-12 VDC
+5 VSB
Note: Total combined output of 3.3 V and 5 V is
Peak currents may last up to 17 seconds with not more than one occurrence per minute
12V1DC and 12V2DC should have separate current limit circuits to meet 240VA safety requirements.
Min.
Current
(amps)
1 8 10
1 14
0.3 18
0.5 17
0 0.3
0 2 2.5
Max.
Current
(amps)
Peak
Current
(amps)
:
Version 2.0
250W Cross Regulation
(5V rail + 3.3V rail vs. 12V)
120
100
80
60
40
20
5V + 3.3V power (watts)
0
0 50 100 150 200 250
12V power (watts)
C
Combined Power
(5V rail + 3.3V rail)
Figure 1. Cross Loading Graph for 250W Configuration
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