SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R11 Design-in Page 64 of 157
2.2.1.4 Guidelines for VCC supply circuit design using a rechargeable battery
Rechargeable Li-Ion or Li-Pol batteries connected to the VCC pins should meet the following prerequisites
to comply with the module VCC requirements summarized in Table 6:
Maximum pulse and DC discharge current: the rechargeable Li-Ion battery with its related output
circuit connected to the VCC pins must be capable of delivering the maximum current occurring during
a transmission at maximum Tx power, as specified in the SARA-R4/N4 series Data Sheet [1]. The
maximum discharge current is not always reported in the data sheets of batteries, but the maximum
DC discharge current is typically almost equal to the battery capacity in Amp-hours divided by 1 hour.
DC series resistance: the rechargeable Li-Ion battery with its output circuit must be capable of avoiding
a VCC voltage drop below the operating range summarized in Table 6 during transmit bursts.
2.2.1.5 Guidelines for VCC supply circuit design using a primary battery
The characteristics of a primary (non-rechargeable) battery connected to VCC pins should meet the
following prerequisites to comply with the module VCC requirements summarized in Table 6:
Maximum pulse and DC discharge current: the non-rechargeable battery with its related output circuit
connected to the VCC pins must be capable of delivering the maximum current consumption occurring
during a transmission at maximum Tx power, as specified in SARA-R4/N4 series Data Sheet [1]. The
maximum discharge current is not always reported in the data sheets of batteries, but the maximum
DC discharge current is typically almost equal to the battery capacity in Amp-hours divided by 1 hour.
DC series resistance: the non-rechargeable battery with its output circuit must be capable of avoiding
a VCC voltage drop below the operating range summarized in Table 6 during transmit bursts.
2.2.1.6 Guidelines for external battery charging circuit
SARA-R4/N4 series modules do not have an on-board charging circuit. Figure 22 provides an example of a
battery charger design, suitable for applications that are battery powered with a Li-Ion (or Li-Polymer) cell.
In the application circuit, a rechargeable Li-Ion (or Li-Polymer) battery cell, that features the correct pulse
and DC discharge current capabilities and the appropriate DC series resistance, is directly connected to the
VCC supply input of the module. Battery charging is completely managed by the Battery Charger IC, which
from a USB power source (5.0 V typ.), linearly charges the battery in three phases:
Pre-charge constant current (active when the battery is deeply discharged): the battery is charged with
a low current.
Fast-charge constant current: the battery is charged with the maximum current, configured by the
value of an external resistor.
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