SARA-N2 / N3 series - System integration manual
UBX-17005143 - R13
Design-in
Page 77 of 95
C1-Public
2.14
Design-in checklists
The following are the most important points for simple checks.
2.14.1
Schematic checklist
The external DC supply circuit must provide a nominal voltage at
VCC
pins within the normal
operating range limits.
The external DC supply circuit must be capable of providing, at
VCC
pins, the specified average
current during a transmission at maximum power with a voltage level above the minimum
operating range limit.
VCC
supply should be clean, with very low ripple/noise.
Do not apply loads that might exceed the maximum available current limit from
V_INT
supply.
Check that voltage level of any connected pin does not exceed the relative operating range.
Capacitance and series resistance must be limited on each SIM signal to match the SIM
specifications.
Insert the suggested capacitors on each SIM signal and low capacitance ESD protections if
accessible.
Check UART signals direction, since the signal names follow ITU-T V.24 recommendation
Provide accessible testpoints directly connected to the following pins:
TXD
,
RXD
,
TXD_FT
,
RXD_FT
,
GPIO1
,
V_INT
,
PWR_ON
and
RESET_N
for diagnostic and FW update purpose.
Provide proper precautions for ESD immunity as required on the application board.
Any external signal connected to the UART interface pin must be tri-stated or set low before
applying
VCC
supply, to avoid latch-up of circuits and let a proper boot of the module.
Any external signal connected to any generic digital interface pin must be tri-stated or set low
when the module is not powered and during the module power-on sequence (at least until the
activation of the
V_INT
output) to avoid latch-up of circuits and let a proper boot of the module.
All unused pins can be left unconnected.
2.14.2
Layout checklist
Check 50
nominal characteristic impedance of the RF transmission line connected to the
ANT
pad (antenna RF input/output interface).
Follow the recommendations of the antenna producer for correct antenna installation and
deployment (PCB layout and matching circuitry).
Ensure no coupling occurs between the RF interface and noisy or sensitive signals (like SIM
signals and high-speed digital lines).
VCC
line should be wide and short.
Route
VCC
supply line away from sensitive analog signals.
Ensure proper grounding.
Optimize placement for minimum length of RF line and closer path from DC source for
VCC
.
Keep routing short and minimize parasitic capacitance on the SIM lines to preserve signal
integrity.
2.14.3
Antenna checklist
Antenna termination should provide 50
characteristic impedance with V.S.W.R at least 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).
Ensure compliance with any regulatory agency RF radiation requirement.
