SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R11 Design-in Page 75 of 157
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. Use as many vias as possible to connect the ground planes
Provide a dense line of vias at the edges of each ground area, in particular along RF and high speed
lines
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 pads also ensures thermal heat sink. This is critical during connection, when
the real network commands the module to transmit at maximum power: correct grounding helps prevent
module overheating.
2.2.2 Generic digital interfaces supply output (V_INT)
2.2.2.1 Guidelines for V_INT circuit design
SARA-R4/N4 series modules provide the V_INT generic digital interfaces 1.8 V supply output, which can be
mainly used to:
Indicate when the module is switched on and it is not in the deep sleep power saving mode (as
described in sections 1.6.1, 1.6.2)
Pull-up SIM detection signal (see section 2.5 for more details)
Supply voltage translators to connect 1.8 V module generic digital interfaces to 3.0 V devices (e.g. see
2.6.1)
Enable external voltage regulators providing supply for external devices
☞ Do not apply loads which might exceed the maximum available current from V_INT supply (see SARA-
R4/N4 series Data Sheet [1]) as this can cause malfunctions in internal circuitry.
☞ V_INT can only be used as an output: do not connect any external supply source on V_INT.
☞ ESD sensitivity rating of the V_INT supply pin is 1 kV (HBM according to JESD22-A114). Higher protection
level could be required if the line is externally accessible and it can be achieved by mounting an ESD
protection (e.g. EPCOS CA05P4S14THSG) close to accessible point.
☞ It is recommended to monitor the V_INT pin to sense the end of the internal switch-off sequence of
SARA-R4/N4 series modules: VCC supply can be removed only after V_INT goes low.
☞ It is recommended to provide direct access to the V_INT pin on the application board by means of an
accessible test point directly connected to the V_INT pin.
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