ATX/ATX12V Power Supply Design Guide
Version 1.1
Page 11
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 cross-
loading: 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.
3.2.3.1. ATX Configurations
Table 4. Typical Power Distribution for a 160 W ATX Configuration
Output
Min.
Current
(amps)
Max.
Current
(amps)
Peak
Current
(amps)
+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
See graph at right for power sharing.
0
10
20
30
40
50
60
70
80
0
20
40
60
80
100
120
+5V & +3.3V com bine d load (W)
+
1
2V lo
ad
(
W
)
