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3. Power
3.1. General Power requirements
COM Express calls for the Module to be powered by a single 12V power rail, with a +/-5% tolerance. The
Basic format Modules are specified in COM.0 Rev. 3.x to support a power input range of 8.55V to 20.0V.
Advantech offer a wide range input even on Compact and Basic Modules. COM Express Modules may
consume significant amounts of power – 25 to 116W is common, and higher levels are allowed by the
standard. Close attention must be paid by the Carrier Board designer to ensure adequate power delivery.
Details are given in the sections below.
If Suspend functions such as Suspend-to-RAM, Suspend-to-disk, wake on power button press, wake on
USB activity, etc. are to be supported, then a 5V Suspend power source must also be provided to the
Module. If Suspend functions are not used, the Module VCC_5V_SBY pins should be left open. On some
Modules, there may be a slight power efficiency advantage to connecting the Module VCC_5V_SBY rail
to VCC_5V rather than leaving the Module pin open.
Please contact Advantech for further details. Carrier Boards typically require other power rails such as
5V, 3.3V, 3.3V Suspend, etc. These may be derived on the Carrier Board from the 12V and 5V Suspend
rails
.
3.2. ATX and AT Power Sequencing Diagrams
A sequence diagram for an ATX style boot from a soft-off state (S5), initiated by a power button press, is
shown in Figure 35 below.
A sequence diagram for an AT style boot from the mechanical off state (G3) is shown in Figure 36
below .
In both cases, the VCC_12V, VCC_5V and VCC_3V3 power lines should rise together in a monotonic
ramp with a positive slope only, and their rise time should be limited. Please refer to the ATX
specification for more details.
