SARA-N2 series - System Integration Manual
UBX-17005143 - R06
Design-in
Page 30 of 82
2.2.1.7
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 sensitive analog signals and
sensitive functional units: it is good practice to interpose at least one layer of PCB ground between
VCC track and other signal routing.
The bypass capacitors in the pF range described in
should be placed as close
as possible to the VCC pins. This is highly recommended if the application device integrates an
internal antenna.
High frequency voltage ripples on the VCC line 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-N2 series modules in the worst case.
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
cellular module, preferably closer to the DC source (otherwise protection functionality may be
compromised).
2.2.1.8
Guidelines for grounding layout design
Good connection of the module GND pins with application board solid ground layer is required for
correct RF performance. It significantly reduces EMC issues and provides a thermal heat sink for the
module.
Connect each GND pin with application board solid GND layer. It is strongly recommended that
each GND pin surrounding VCC pins have one or more dedicated via down to the application board
solid ground layer.
The VCC supply current flows back to main DC source through GND as ground current: provide
adequate return path with suitable uninterrupted ground plane to main DC source.
It is recommended to implement one layer of the application board as ground plane as wide as
possible.
If the application board is a multilayer PCB, then all the board layers should be filled with GND plane
as much as possible and each GND area should be connected together with complete via stack
down to the main ground layer of the board.
If the whole application device is composed by more than one PCB, then it is required to provide a
good and solid ground connection between the GND areas of all the different PCBs.
Good grounding of GND pins also ensures thermal heat sink. This is critical during call connection,
when the real network commands the module to transmit at maximum power: proper grounding
helps prevent module overheating.
