User Manual

LARA-R2 series - System Integration Manual
UBX-16010573 - R02 Objective Specification Design-in
Page 65 of 148
2.2 Supply interfaces
2.2.1 Module supply (VCC)
2.2.1.1 General guidelines for VCC supply circuit selection and design
All the available VCC pins have to 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.
LARA-R2 series modules must be supplied through the VCC pins by a proper DC power supply that should
comply with the module VCC requirements summarized in Table 6.
The proper DC power supply can be selected according to the application requirements (see Figure 25) between
the different possible supply sources types, which most common ones 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 25: 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 2.2.1.2 and 2.2.1.6, 0, 2.2.1.12 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 2.2.1.3 and 2.2.1.6, 0, 2.2.1.12 for specific design-in.
If LARA-R2 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 2.2.1.4, 2.2.1.6, 2.2.1.7, 0, 2.2.1.12 for 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 has 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 an high nominal voltage (e.g. ~12 V), whereas a linear charger is