Integration Manual
SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 55 of 119
2.2.1.12 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 pad
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. 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
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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.
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V_INT can only be used as an output: do not connect any external supply source on V_INT.
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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.
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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.
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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.