Intel ATX 3.0, Design Manual

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Processor
Configurations
18 336521
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 5.2.2.5 +12 V
Power Connector. 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 d12 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.
Three examples of modular designs are shown below. The orange box in each picture
identifies the connectors on the power supply 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