Congatec COM Express conga-TC175 User Manual page 27

The three typical usage scenarios for a carrier board design are:
• Connect PWR_OK to the "power good" signal of an ATX type power supply.
• Connect PWR_OK to the last voltage regulator in the chain on the carrier board.
• Simply pull PWR_OK with a 1k resistor to the carrier board 3.3V power rail.
With this solution, make sure that before the 3.3 V goes up, all carrier board hardware is fully powered and all clocks are stable.
The conga-TC175 supports the controlling of ATX-style power supplies. If you do not use an ATX power supply, do not connect the conga-
TC175 pins SUS_S3/PS_ON, 5V_SB, and PWRBTN# on the conga-TC175.
SUS_S3#/PS_ON#
The SUS_S3#/PS_ON# (pin A15 on the A-B connector) signal is an active-low output that can be used to turn on the main outputs of an ATX-
style power supply. To accomplish this the signal must be inverted with an inverter/transistor that is supplied by standby voltage and is located
on the carrier board.
PWRBTN#
When using ATX-style power supplies PWRBTN# (pin B12 on the A-B connector) is used to connect to a momentary-contact, active-low
debounced push-button input while the other terminal on the push-button must be connected to ground. This signal is internally pulled up
to 3V_SB using a 10k 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.
Standard 12V Power Supply Implementation Guidelines
12 volt input power is the sole operational power source for the conga-TC175. The remaining necessary voltages are generated internally on
the module using onboard voltage regulators.
A carrier board designer should be aware of the following important information when designing a power supply for a conga-TC175 application:
• We noticed that occasionally problems occur when using a 12V 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. This problem is rare but has been observed in some mobile power supply applications. To ensure that this
problem does not occur, observe the power supply rise waveform with an oscilloscope to determine if the rise is indeed monotonic and
does not have any dips. Do this during the power supply qualification phase to ensure that the above mentioned problem does not occur
in the application. For more information about this issue visit www.formfactors.org and view page 25 figure 7 of the document "ATX12V
Power Supply Design Guide V2.2".
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