microATX Motherboard Interface Specification

Version 1.2

Page 21

3.3 Voltage Tolerances

Tolerance for the motherboard power rails should comply to the values listed in Table 7.

Table 7: Voltage Tolerances

Parameter Range Min. Nom. Max. Unit

+12 VDC ± 5 % +11.40 +12.00 +12.60 Volts

+ 5 VDC ± 5 % +4.75 +5.00 +5.25 Volts

+3.3 VDC ± 5 % +3.14 +3.30 +3.47 Volts

-12 VDC ± 10 % -10.80 -12.00 -13.20 Volts

+ 5 VSB ± 5 % +4.75 +5.00 +5.25 Volts

3.4 Optional 6-pin Power Connector

An optional 6-pin connector from the power supply can be used for such functions as fan monitoring, fan

control, IEEE-1394 power source, and a remote 3.3V sense line. Although this connector is not required for

ATX compliance, it can add benefits that are compelling for a full-featured system:

• The fan monitor features add the ability to monitor and detect fan failures.

• A built-in fan control allows the motherboard to request fan shutdown when the system goes into a sleep

or suspend mode.

• Fan speed control is possible to allow for slower fan speeds during low power usage.

Figure 10 shows the pinout of the optional power connector. The PC board connector should be implemented

with a Molex 39-30-1060 or equivalent connector. This mates with the power supply connector, Molex 39-

01-2060 or equivalent. The exact location of this connector on the motherboard is not specified but should be

near the main connector for convenience.

Proper implementation of FanM, FanC, 3.3V Sense, 1394V, and 1394R is discussed below. Except for FanM

and 3.3Vsense (see note below figure), the signals should be implemented according to these specifications if

an optional connector is used.

1394R FanM*

1394V

FanC

5 2

6 3

Reserved 3.3V Sense*

Figure 10: 6-pin Optional Power Supply Connector Configuration

(optional for microATX; used in ATX 2. 1 or higher)

Note:

* All signals that can be carried on the 6-pin connector are not required or available on some power supplies. These

optional signals are not available in the SFX12V or TFX12V (Thin Form Factor with 12V Connector) power

supplies: FanM and 3.3V Sense.