Integration Manual

SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 54 of 119
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☞ ESD sensitivity rating of the VCC supply pins is 1 kV (HBM according to JESD22-A114). 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 Figure 28
• 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 2.2.1.10 should be placed
close to the 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 Figure 27 and Table 19 should be placed as 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 SARA-R4/N4 series 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)
SARA
VCC
ANT
Ant enna
NOT OK
Ant enna
SARA
VCC
ANT
OK
Ant enna
SARA
VCC
ANT
NOT OK
Figure 28: VCC line routing guideline for designs integrating an embedded antenna