User`s guide

Power Control4.1.11

PWR_OK

Power OK from main power supply. A high value indicates that the power is good. Using this input is optional. Through the use of an internal

monitor on the +12V ± 5% input voltage and/or the internal power supplies the conga-B915 module is capable of generating its own power-on

reset. According to the COM Express™ Specication PWR_OK is a 3.3V signal.

The conga-B915 provides support for controlling ATX-style power supplies. When not using an ATX power supply then the conga-B915’s pins

SUS_S3/PS_ON, 5V_SB, and PWRBTN# should be left unconnected.

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. In order 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 modications made in BIOS settings or by system software.

Power Supply Implementation Guidelines

12 volt input power is the sole operational power source for the conga-B915. The remaining necessary voltages are internally generated on

the module using onboard voltage regulators. A baseboard designer should be aware of the following important information when designing a

power supply for a conga-B915 application:

It has also been noticed that on some occasions 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. 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

qualication phase therefore ensuring that the above mentioned problem doesn’t arise in the application. For more information about this

issue visit www.formfactors.org and view page 25 gure 7 of the document “ATX12V Power Supply Design Guide V2.2”.