System information

9.4 Power Consumption
the USB-IF
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has instituted a Compliance Program that provides reasonable measures of
acceptability [105]. The USB-IF provides a compliance test tool, the USB Command Verifier
(USBCV) which evaluates High, Full and Low-speed USB devices for conformance to the
USB Device Framework, Hub device class, HID class, and OTG specifications [105]. The
USB devices provided by the CHARM are test with the USB Command Verifier. The
CHARM successfully pass the the USB Device Framework, HID class and the mass storage
class verification test
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.
9.4 Power Consumption
By the reason, the CHARM is a PCI device, and it is subject to the PCI standard. The PCI
Conventional Specification limits the power consumption for any PCI boards to 25 watts
[40]. But many systems cannot provide the full 25 watts per connector. PCI boards which
consume more than 10 watts should be powered up in a power saving mode.
Voltage Current Power
CHARM-B card 5V 0,62A 3,10W
CHARM-C card 5V 0,59A 2,95W
CHARM-C card 3,8V 0,56A 2,13W
PCI power limit 5V 5A 25W
PCI standby power limit 3,3V 0,374A ∼1,24W
ATX standby power limit 5V 2,5A 12,5W
Table 9.5: Power consumption and power limitation of the CHARM card.
The CHARM consumes less than 10 watts and in addition, it has extra power sources.
The CHARM can be powered by an external power supply or by a Wake On LAN plug.
The interface for the external power supply is accessible at the card bracket. Wake On LAN
(WOL) is an industry standard of remote power management of computer systems. The
WOL plug soldered on motherboards provides a standby power source. It is served by the
power supply of the computer. By the matter of facts, the ATX standard specifies among
others things the form factors, connectors and voltage limits of power supplies for computer
systems. The maximum power consumption of the 5V standby power of ATX power supplies
is limited to 12,5W [106, 107]. Table 9.5 gives an overview of the power consumption
requirements. Additionally, the table lists the power consumption of the CHARM models
B and C. Since 1999 the standby power for expansion cards has been able to be obtained by
the PCI bus [59]. But the PCI standby power provides less power than it is consumed by
the CHARM. There are some opportunities to reduce power consumption of the CHARM.
It is powered by a 5V power source. But the main hardware units on the card need a
voltage equal or less than 3.3V. The 5V power source is used for both the PCI bus switch
and the USB host function. However, the PCI bus switch can obtain the voltage from the
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Universal Serial Bus Implementers Forum [105].
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The USBCV version 1.3 was used for the verification.
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