Doc. No: Unex-QSG-21-003
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© 2023 Unex Technology Corporation – Company Confidential
lower the impedance of the 5V power rail.
9.2.
Power Sequence
•
5V should be supplied prior to 3.3 Vaux.
•
If 3.3 Vaux is fed before 5V, user should toggle the EX_RSTn signal after 5V is
supplied.
•
If it is intended to save power when the SOM-352 is not in use, it is suggested to
pull low the EX_RSTn/PERST# pin instead of cutting off 5V power. Once the
EX_RSTn/PERST# pin is pulled low, the SOM-352 will enter standby mode, and
the power consumption will reduce to 10mA in about 10 seconds.
9.3.
Brown Out
•
If the 5V power supply drops below 3.5V, the SOM-352 will enter standby mode.
•
A SOM in standby mode will stay in this mode until reset.
•
Once the power supply returns to normal, the SOM-352 can reboot into normal
operation with the rising edge of PERST# or EX_RSTn signal.
9.4.
Grounding
•
Ensure good GND connection between the ground of the module and the ground of
the system board.
•
Grounding of the external components (e.g., capacitors) should be connected to
the same reference ground of the module and not just on the top layer, use more
than one via whenever possible to ensure good GND connection.
9.5.
USB Data Lines
The SOM-352 mPCIe module includes a Universal Serial Bus (USB) transceiver, which
operates at USB high-speed (480 Mbits/s). It is compliant with the USB 2.0 specification
and can be used for control and data transfers as well as for diagnostic monitoring and
firmware upgrade.
The USB port is typically the main interface between the SOM-352 mPCIe module and
OEM hardware. Since the USB_D+ and USB_D- signals have a clock rate of 240 MHz, the
signal traces must be routed carefully. Minimize trace lengths, number of vias, and
capacitive loading.
The layout guidelines for the USB data lines (mPCIe pin 36, 38) is listed below. And a
