u-blox LEXI-R422, Руководство по системной интеграции

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LEXI-R422 - System integration manual
UBX-23007449 - R02 Design-in Page 33 of 108
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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. Application design shall 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.
LEXI-R422 modules must be sourced through the VCC pins with a suitable DC power supply that
should meet the following prerequisites to comply with the modules VCC requirements summarized
in Table 6 .
The appropriate DC power supply can be selected according to the application requirements (see
Figure 16 ) 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 16: VCC supply concept selection
The switching step-down regulator is the typical choice when primary supply source has a nominal
voltage much higher (e.g. greater than 5 V) than the operating supply voltage of LEXI-R422. 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 section
2.2.1.2 for design-in.
The use of an LDO linear regulator becomes convenient for a primary supply with a relatively low
voltage (e.g. less or equal 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 section
2.2.1.3 for design-in.
If LEXI-R422 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 , 2.2.1.5 , 2.2.1.6 and 2.2.1.7 for specific design-
in.