Compaq COM Express Extension - Manual (Page 15)

5 Hardware extensions
Copyright © COM Express™ Extension
Specification Rev 013
15
5 Hardware extensions
Wide Range Input Power for basic, extended and micro form factor
Wide range input power: +8.5VDC to +18VDC
It allows direct operation from 108 nominal 3 cell lithium ion battery pack to 4-cell lithium-ion battery
packs (16,8 V fully charged)
Additionally, Smart Battery Support offers a great base for a mobile application. See Software section
for more details
5.1.1 Wide Range Input Power for nano SmallFormFactor (SFF)
The nano modules should use a single main power rail with a wide range power supply of 5V
to +14V+/-5% (4,75V to 14,7V)
Two additional rails are specified, a +5V standby power rail and a +3V battery input to power
the module real-time clock (RTC) circuit in the absence of other power sources. The +5V
standby rail could be left unconnected on the carrier board if the standby functions are not
required by the application. Likewise, the +3V battery input may be left open if the
application does not require the RTC to keep time in the absence of the main and standby
sources. There may be module specific concerns regarding storage of system setup parameters
that may be affected by the absence of the +5V standby and / or the +3V battery.
The rationale for this power-delivery scheme is:
• Module pins are scarce. It is more pin-efficient to bring power in on a higher
voltage rail.
• Single supply operation is attractive to many users.
• Lithium ion battery packs for mobile systems are most prevalent with a +14.4V
output. This is well suited for the +12V main power rail.
• Contemporary chipsets have no power requirements for +5V other than to provide a
reference voltage for +5V tolerant inputs. No COM Express™ module pins are
allocated to accept +5V except for the +5V standby pins. In the case of an ATX
supply, the switched (non standby) +5V line would not be used for the COM
Express™ module, but it might be used elsewhere on the carrier board.