LENA-R8 series - System integration manual
UBX-22015376 - R02
Design-in
Page 33 of 116
C1-Public
2.2
Cellular power management
2.2.1
Cellular supply input (VCC)
2.2.1.1
General guidelines for cellular VCC supply circuit selection and design
All of 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 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.
LENA-R8 series modules cellular system must be supplied through the
VCC
pins by a proper DC power
supply that should comply with the module
VCC
requirements summarized in
The appropriate DC power supply can be selected according to the application requirements (see
). The most common supply sources are the following:
•
Switching regulator
•
Low Drop-Out (LDO) linear regulator
•
Rechargeable Lithium-ion (Li-ion) or Lithium-ion polymer (Li-Pol) battery
•
Primary (disposable) battery
Main supply
available?
Battery
Li-Ion 3.7 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 17: VCC supply concept selection
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
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
for the specific design-in.
If LENA-R8 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
for the specific design-in.
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 must be designed to prevent
over-voltage on the
VCC
pins, and it should be selected according to the application requirements: a
