SARA-N2 / N3 series - System integration manual
UBX-17005143 - R13
Design-in
Page 33 of 95
C1-Public
2.2.1.3
Guidelines for VCC supply circuit design using a primary battery
The characteristics of a battery connected to
VCC
pins should meet the following prerequisites to
comply with the module
VCC
requirements summarized in
•
Maximum pulse and DC discharge current
: the non-rechargeable battery with its output circuit
must be capable of delivering to
VCC
pins the specified average current during a transmission at
maximum power (see the SARA-N2 series data sheet
and SARA-N3 series data sheet
for
more details). The antenna matching influences the current consumption; for this reason, the
current consumption at maximum Tx power with the intended antenna (i.e. on the final application
board) should be used to characterize the battery maximum pulse requirements.
The maximum DC discharge current is not always reported in battery data sheets, but it is typically
almost equal to the battery capacity in Amp-hours divided by 1 hour.
•
DC series resistance
: the non-rechargeable battery with its output circuit must be capable to limit
as much as possible the DC resistance provided on the
VCC
supply line.
The LiSOCl2 (Lithium Thionyl Chloride Batteries) is currently the best technology available for NB-IoT
applications since it provides:
•
Very low self-discharge behavior and resulting ability to last longer
•
Highest specific energy per unit weight and energy density per unit volume
•
Wide operating temperature range
For the selection of the proper battery type, the following parameters should be taken into account:
•
Capacity: > 3 Ah
•
Continuous current capability: ~400 mA (the consumption of whole application with the actual
antenna should be considered)
•
Temperature range: -20 °C to +85 °C
•
Capacity vs temperature behavior: battery capacity is highly influenced by the temperature. This
must be considered to properly estimate the battery life time
•
Capacity vs discharge current performance
•
Voltage vs temperature behavior: the battery voltage typically decreases at low temperatures
values (for example, in the -10 °C / -20 °C range). In all the temperature conditions the battery
voltage must always be above the SARA-N2 minimum extended operating voltage level
•
Voltage vs pulse duration behavior: this information is typically not provided by battery
manufacturers, and many batteries reach too low voltage values during a long pulse. It is
recommended to execute stress tests on battery samples to verify the voltage behavior as a
function of the pulse duration and to guarantee that the battery voltage is always above the
minimum extended operating voltage level of SARA-N2 series.
•
Construction technology: spiral wound
batteries are generically preferred over the bobbin
construction
o
This technology typically supports high current pulses without the need for supercaps
o
A bobbin type battery usually does not support the current pulse
