LEXI-R422 - System integration manual
UBX-23007449 - R02
Design-in
Page 46 of 108
C1-Public
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ESD sensitivity rating of the
VCC
supply pins is 1 kV (HBM according to JS-001-2017). Higher
protection level can be required if the line is externally accessible on the application board, e.g. if
accessible battery connector is directly connected to the supply pins. Higher protection level can
be achieved by mounting an ESD protection (e.g. EPCOS CA05P4S14THSG varistor) close to
accessible point.
2.2.1.11
Guidelines for VCC supply layout design
Good connection of the module
VCC
pins with DC supply source is required for correct RF
performance. Guidelines are summarized in the following list:
•
All the available
VCC
pins must be connected to the DC source.
•
VCC
connection must be as wide as possible and as short as possible.
•
Any series component with Equivalent Series Resistance (ESR) greater than few milliohms must
be avoided.
•
VCC
connection must be routed through a PCB area separated from RF lines / parts, sensitive
analog signals and sensitive functional units: it is good practice to interpose at least one layer of
PCB ground between the
VCC
track and other signal routing.
•
VCC
connection must be routed as far as possible from the antenna, in particular if embedded in
the application device: see
•
Coupling between
VCC
and digital lines, especially USB, must be avoided.
•
The tank bypass capacitor with low ESR for current spikes smoothing described in section
VCC
pins; if the main DC source is a switching DC-DC
converter, place the large capacitor close to the DC-DC output and minimize
VCC
track length,
otherwise consider using separate capacitors for DC-DC converter and module tank capacitor.
•
The bypass capacitors in the pF range described in
close as possible to the
VCC
pins, where the
VCC
line narrows close to the module input pins,
improving the RF noise rejection in the band centered on the self-resonant frequency of the pF
capacitors: this is highly recommended if the application device integrates an internal antenna.
•
Since
VCC
input provide the supply to RF power amplifiers, voltage ripple at high frequency may
result in unwanted spurious modulation of transmitter RF signal; this is more likely to happen with
switching DC-DC converters, in which case it is better to select the highest operating frequency
for the switcher and add a large L-C filter before connecting to the LEXI-R422 modules in the worst
case.
•
Shielding of switching DC-DC converter circuit, or at least the use of shielded inductors for the
switching DC-DC converter, may be considered since all switching power supplies may potentially
generate interfering signals as a result of high-frequency high-power switching.
•
If
VCC
is protected by transient voltage suppressor to ensure that the voltage maximum ratings
are not exceeded, place the protecting device along the path from the DC source toward the
module, preferably closer to the DC source (otherwise protection function may be compromised).
Antenna
NOT OK
Antenna
OK
Antenna
NOT OK
LEXI
VCC
ANT
LEXI
VCC
ANT
LEXI
VCC
ANT
Figure 27: VCC line routing guideline for designs integrating an embedded antenna
