to the 5V_SB supply voltage through the use of a 1K resistor. Usually there is a pull-up
resistor internally implemented in the power supply itself yet it is also good practice to
implement a footprint for the pull-up resistor in the baseboard circuitry.
PWRBTN#
When using ATX-style power supplies PWRBTN# (pin 7 on the X4 connector) is used to
connect to a momentary-contact, active-low pushbutton input while the other terminal on
the pushbutton must be connected to ground. This signal is XTX™ internally pulled up
to 5V_SB using a 4k7 resistor. When PWRBTN# is asserted it indicates that an
operator wants to turn the power on or off. The response to this signal from the system
may vary as a result of modifications made in BIOS settings or by system software.
Power Supply Implementation Guidelines
5 volt input power is the sole operational power source for the conga-X945/XA945. The
remaining necessary voltages are internally generated on the module using onboard
power supplies. A baseboard designer should be aware of the following important
information when designing a power supply for a conga-X945/XA945 application:
•
As mentioned earlier in section 4.1.4 the conga-X945/XA945 is capable of generating
an onboard 3.3V supply with an output current that is limited to 500mA. If an external
device requires more then this 500mA limit then it's necessary to design a 3.3V
supply into the baseboard.
Caution
It is not possible to connect an external 3.3V supply to the onboard generated 3.3V
supply pins on the conga-X945/XA945 module. This will cause a current cross-flow and
may result in either a system malfunction and/or damage to the external power supply
and the module.
•
Sometimes when designing baseboards, baseboard designers choose to fuse power
to some external devices such as keyboards or USB devices by using solid-state or
polyswitch overcurrent protection devices. This results in the protective devices
typically only opening after they pass several times their rated current for long
periods of time. When the application power supply is incapable of generating the
necessary current needed to open these protective devices it's possible that the
application crashes as a result of an external fault and therefore will reduce the
applications reliability as well as make a fault diagnosis of the application difficult.
•
It has also been noticed that on some occasions problems occur when using a 5V
power supply that produces non monotonic voltage when powered up. The problem
is that some internal circuits on the module (e.g. clock-generator chips) will generate
their own reset signals when the supply voltage exceeds a certain voltage threshold.
A voltage dip after passing this threshold may lead to these circuits becoming
confused resulting in a malfunction. It must be mentioned that this problem is quite
rare but has been observed in some mobile power supply applications. The best way
to ensure that this problem is not encountered is to observe the power supply rise
waveform through the use of an oscilloscope to determine if the rise is indeed
monotonic and does not have any dips. This should be done during the power supply
qualification phase therefore ensuring that the above mentioned problem doesn't
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