u-blox SARA-G3 Series, Руководство по системной интеграции

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SARA-G3 series - System Integration Manual
UBX-13000995 - R06 Objective Specification Design-in
Page 92 of 218
2.1 Supply interfaces
2.1.1 Module supply (VCC)
2.1.1.1 General guidelines for VCC supply circuit selection and design
VCC pins are internally connected, but connect all the available pads to the external supply to minimize
the power loss due to series resistance.
GND pins are internally connected but connect all the available pads 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.
SARA-G3 modules must be supplied through the
VCC pins by a proper DC power supply that should
meet the following prerequisites to comply with the module VCC requirements summarized in Table 6Table
6 .
The proper DC power supply can be selected according to the application requirements (see Figure
26Figure 26 ) 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 26: VCC supply concept selection
The 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 SARA-G3 modules 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.
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.
If SARA-G3 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