SARA-N2 / N3 series - System integration manual
UBX-17005143 - R13
Design-in
Page 31 of 95
C1-Public
2.2
Supply interfaces
2.2.1
Module supply input (VCC)
2.2.1.1
General guidelines for VCC supply circuit selection and design
All the available
VCC
pins must be connected to the external supply minimizing the power loss due to
series resistance.
GND
pins are internally connected but connect all the available pins to a solid ground on the
application board, since a good (low impedance) connection to external ground can minimize power
loss and improve RF and thermal performance.
SARA-N2 / N3 series modules must be supplied through the
VCC
pins by a proper DC power supply
that should comply with the module
VCC
The proper DC power supply can be selected according to the application requirements (see
between the different possible supply sources types, which most common ones are the following:
•
Primary (disposable) battery
•
Rechargeable Lithium-ion (Li-Ion) or Lithium-ion polymer (Li-Pol) battery
•
Switching regulator
•
Low Drop-Out (LDO) linear regulator
Main supply
available?
Battery
LiSOCl
2
3.6 V
Linear LDO
regulator
Main supply
voltage > 5V?
Switching step-down
regulator
No, portable device
No, less than 5 V
Yes, greater than 5 V
Yes, always available
Figure 13: VCC supply concept selection
The NB-IoT technology is primarily intended for battery powered applications. A Lithium Thionyl
Chloride (LiSOCl
2
) battery directly connected to
VCC
pins is the usual choice for battery-powered
devices. See sections
and
for specific design-in.
The DC/DC switching step-down regulator is the typical choice when the available primary supply
source has a nominal voltage much higher (e.g. greater than 5 V) than the modules
VCC
operating
supply voltage. The use of switching step-down provides the best power efficiency for the overall
application and minimizes current drawn from the main supply source. See sections
and
for specific design-in.
The use of an LDO linear regulator becomes convenient for a primary supply with a relatively low
voltage (e.g. less than 5 V). In this case the typical 90% efficiency of the switching regulator
diminishes the benefit of voltage step-down and no true advantage is gained in input current savings.
On the opposite side, linear regulators are not recommended for high voltage step-down as they
dissipate a considerable amount of energy in thermal power. See sections
The use of rechargeable batteries is not the typical solution for NB-IoT applications, but it is feasible
to implement a suitable external charger circuit. The charger circuit has to be designed to prevent
over-voltage on
VCC
pins of the module, and it should be selected according to the application
requirements: a DC/DC switching charger is the typical choice when the charging source has an high
