SARA-N2 / N3 series - System integration manual
UBX-17005143 - R13
Design-in
Page 32 of 95
C1-Public
nominal voltage (e.g. ~12 V), whereas a linear charger is the typical choice when the charging source
has a relatively low nominal voltage (~5 V). If both a permanent primary supply / charging source (e.g.
~12 V) and a rechargeable back-up battery (e.g. 3.7 V Li-Pol) are simultaneously available in the
application as possible supply sources, then a proper charger / regulator with integrated power path
management function can be selected to supply the module while simultaneously and independently
charging the battery.
The usage of more than one DC supply at the same time should be carefully evaluated: depending on
the supply source characteristics, different DC supply systems can be mutually exclusive.
The usage of supercapacitors on the
VCC
supply line is generally not recommended since these
components are highly temperature sensitive and may increase current leakages draining the battery
faster.
The following sections highlight some design aspects for power-supply scenarios, providing
application circuit design-in compliant with the module
VCC
requirements summarized in
☞
For the additional specific requirements applicable during the integration of SARA-N211 and
SARA-N310 modules in devices intended for use in potentially explosive atmospheres, see section
2.2.1.2
Guidelines to optimize power consumption
The NB-IoT technology is primarily intended for applications that require small amount of data
exchange per day (i.e. few bytes in uplink and downlink per day) and these are typically battery
powered. Depending on the application type, an operating life of 5 to 15 years is usually required. For
these reasons, the whole application board should be optimized in terms of current consumption and
should carefully take into account the following aspects:
•
Minimize current leakages on the power supply line
•
Optimize the antenna matching since an un-matched antenna leads to higher current
consumptions
•
Use an application processor with UART interface working at the same level of the UART interface
of the module (
VCC
, i.e. ~3.3 ÷ 3.6 V, for SARA-N2 modules;
V_INT
, i.e. 1.8 V or 2.8 V, for SARA-N3
series modules), in order to avoid voltage translators on the UART interface
•
The application processor should go in standby (or lowest power consumption mode) as soon as
the SARA-N2 / N3 series module enters the deep-sle
ep mode and there’s no more data to be
transmitted: the module will automatically enter the deep-sleep mode whenever possible to limit
current consumption and avoid further network registration procedures each time there is an up-
link message to be transmitted.
•
The application processor can monitor the
V_INT
level to sense when SARA-
N2 modules’
radio is
on or off, or to sense when a SARA-N3 module is on or off
•
The application processor can detect the presence of down-link messages monitoring the line
providing the Ring Indicator functionality (
CTS
pin on SARA-N2 modules,
RI
pin on SARA-N3 series
modules), notifying incoming data received by the module or an URC event.
•
Possibility to request new network timers and select the optimum set of values depending on the
intended application use case
