Integration Manual

LISA-U2 series - System Integration Manual
UBX-13001118 - R25 Design-In Page 118 of 182
 All unused pins can be left floating on the application board except the PWR_ON pin (must be
connected to V_BCKP by a pull-up resistor) and RSVD pin number 5 (must be connected to
GND).
2.1.2 Layout checklist
The following are the most important points for a simple layout check:
 Check the 50  nominal characteristic impedance of the RF transmission line connected to the
ANT pad (main RF input/output) and to the ANT_DIV pad (RF input for Rx diversity).
 Follow the recommendations of the antenna producer for correct antenna installation and
deployment (PCB layout and matching circuitry).
 Ensure no coupling occurs with other noisy or sensitive signals (e.g. SIM signals).
 The VCC line should be as wide and as short as possible.
 Provide the suggested series ferrite bead and bypass capacitors close to the VCC pins
implementing the recommended layout and placement, especially if the application device
integrates an internal antenna.
 Route the VCC supply line away from sensitive analog signals.
 The high-power audio outputs lines on the application board must be wide enough to minimize
series resistance.
 Ensure proper grounding.
 Consider “No-routing” areas for the Data Module footprint.
 Optimize placement for minimum length of RF line and closer path from the DC source for VCC.
 Design the USB_D+ / USB_D- connection as 90  differential pair, with 30  common mode
impedance.
 Keep routing short and minimize parasitic capacitance on the SPI lines to preserve signal
integrity.
 Keep routing short and minimize parasitic capacitance on CODEC_CLK line to preserve signal
integrity.
2.1.3 Antenna checklist
 Antenna should have 50  impedance, VSWR less than 3:1 (recommended 2:1) on operating
bands in deployment geographical area.
 Follow the recommendations of the antenna producer for correct antenna installation and
deployment (PCB layout and matching circuitry).
 Follow the additional guidelines for products marked with the FCC logo (United States only)
reported in section 1.15.2.2
 The antenna connected to the ANT pad should have built-in DC resistor to ground to get proper
antenna detection functionality.
 The antenna for the Rx diversity connected to the ANT_DIV pin should be carefully separated
from the main Tx/Rx antenna connected to the ANT pin: the distance between the two antennas
should be at least greater than half a wavelength of the lowest used frequency (i.e. distance
greater than ~20 cm, for 2G/3G low bands) to distinguish between different multipath channels,
for proper spatial diversity implementation.