SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R11
Design-in
Page 54 of 157
side, linear regulators are not recommended for high voltage step-down as they dissipate a considerable
amount of energy in thermal power. See section
If SARA-R4/N4 series modules are deployed in a mobile unit where no permanent primary supply source is
available, then a battery will be required to provide
VCC
. A standard 3-cell Li-Ion or Li-Pol battery pack
directly connected to
VCC
is the usual choice for battery-powered devices. During charging, batteries with
Ni-MH chemistry typically reach a maximum voltage that is above the maximum rating for
VCC
, and should
therefore be avoided. See sections
Keep in mind that the use of rechargeable batteries requires the implementation of a suitable charger
circuit, which is not included in the modules. The charger circuit needs to be designed to prevent over-
voltage on
VCC
pins, and it should be selected according to the application requirements. A DC/DC
switching charger is the typical choice when the charging source has a high 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 available at the same time as possible supply source, then a suitable charger
/ regulator with integrated power path management function can be selected to supply the module while
simultaneously and independently charging the battery. See sections
in.
An appropriate primary (not rechargeable) battery can be selected taking into account the maximum current
specified in the SARA-R4/N4 series Data Sheet
during connected mode, considering that primary cells
might have weak power capability. See section
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 result as mutually exclusive.
The selected regulator or battery must be able to support with adequate margin the highest averaged
current consumption value specified in the SARA-R4/N4 series Data Sheet
The following sections highlight some design aspects for each of the supplies listed above providing
application circuit design-in compliant with the module
VCC
requirements summarized in
2.2.1.2
Guidelines for VCC supply circuit design using a switching regulator
The use of a switching regulator is suggested when the difference from the available supply rail source to
the
VCC
value is high, since switching regulators provide good efficiency transforming a 12 V or greater
voltage supply to the typical 3.8 V value of the
VCC
supply.
The characteristics of the switching regulator connected to
VCC
pins should meet the following prerequisites
to comply with the module
VCC
requirements summarized in
