LISA-U1 series - System Integration Manual
3G.G2-HW-10002-3
Preliminary
Design-In
Page 95 of 125
Figure 51: Layer 4 (bottom layer) of u-blox approved interface board for LISA-U1 series modules
The antenna must not exceed 3 dBi gain to preserve the original u-blox FCC ID.
The antenna must be installed and operated with a minimum distance of 20 cm from all persons and
must not be co-located or operating in conjunction with any other antenna or transmitter.
Under the requirements of FCC Section 15.212(a)-iv, the module must contain a permanently attached antenna,
or contain an unique antenna connector, and be marketed and operated only with specific antenna(s).
In accordance with FCC Section 15.203, the antenna should use a unique coupling connector to the
approved reference design for LISA-U1 series modules, to ensure that the design will not be deployed
with antenna of different characteristic from the approved type.
The use of standard SMA type connector is not permitted, as its standard usage allows easy replacement of the
attached antenna. However RP-SMA (Reverse-Polarized-SMA) connector type fulfills the minimum requirements
to prevent exchangeability of antenna on the reference design.
2.2.1.2
Main DC supply connection
The DC supply of LISA-U1 series modules is very important for the overall performance and functionality of the
integrated product. For detailed description, check the design guidelines in section 1.5.2. Some main
characteristics are:
VCC
pins are internally connected, but it is recommended to use all the available pins in order to minimize
the power loss due to series resistance
VCC
connection may carry a maximum burst current in the order of 2.5 A. Therefore, it is typically
implemented as a wide PCB line with short routing from DC supply (DC-DC regulator, battery pack, etc)
The module automatically initiates an emergency shutdown if supply voltage drops below hardware
threshold. In addition, reduced supply voltage can set a worst case operation point for RF circuitry that may
behave incorrectly. It follows that each voltage drop in the DC supply track will restrict the operating margin
at the main DC source output. Therefore, the PCB connection must exhibit a minimum or zero voltage drop.
Avoid any series component with Equivalent Series Resistance (ESR) greater than a few milliohms
Given the large burst current,
VCC
line is a source of disturbance for other signals. Therefore route
VCC
through a PCB area separated from sensitive analog signals. Typically it is good practice to interpose at least
one layer of PCB ground between
VCC
track and other signal routing
The
VCC
supply current supply flows back to main DC source through GND as ground current: provide
adequate return path with suitable uninterrupted ground plane to main DC source
