Doc. No: Unex-QSG-21-003
15/23
A printed version of this document is an uncontrolled copy
© 2021 Unex Technology Corporation – Company Confidential
Position
Name
ON Function
OFF Function
SW1.7
TRIGGER_SW
Trigger when tamper SW
close to ground (1KΩ PU)
Trigger with tamper SW
open from 3.3V (32KΩ PD)
SW1.8
BOOT_SW
Boot from NAND
Boot from USB0
9.
Design-in Guidelines
The SOM-301(v2)/SOM-351 pinout is compatible with most standard PCIe mini card
interfaces. However, it may need to be fed with 5V DC power and connecting other I/O
interfaces through an external cable when installed on an existing mPCIe system board. A
customized PCIe mini card pinout can help user to get rid of the extra cable and to rely on
the PCIe mini card interface alone. A design-in system board solution may provide
improved reliability, simpler installation, and cost saving to the overall system.
9.1.
Power Line Traces
•
Power line traces should be as wide as possible, in order to reduce impedance of
these lines.
•
Crossing by any other lines of upper or lower layer should also be avoided.
•
The maximum power consumption occurs during RF transmission. A typical
transmitting frame lasts 1-2ms.
•
It is recommended to keep the 5V supply current no less than 2A (continuous) to
keep RF performance from degradation.
•
If the SOM-301(v2)/SOM-351 halts or resets while performing a V2X RF
transmission, it is recommended to add a bulk capacitor on the 5V trace near the
mPCIe connector to 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-301(v2)/SOM-351 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-301(v2)/SOM-351 will
enter standby mode, and the power consumption will reduce to 10mA in about 10
seconds.
