SARA-R4 series - System Integration Manual
UBX-16029218 - R06
Design-in
Page 39 of 102
2.2.1.4
Guidelines for VCC supply circuit design using a rechargeable Li-Ion or Li-Pol 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
SARA-R4 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 (disposable) 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 series
Data Sheet
[1]. The maximum
discharge current is not always reported in the data sheets of batteries, but the max 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 series modules do not have an on-board charging circuit. Figure 13 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 proper pulse and DC
discharge current capabilities and proper 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.
Constant voltage
: when the battery voltage reaches the regulated output voltage, the Battery Charger IC
starts to reduce the current until the charge termination is done. The charging process ends when the
charging current reaches the value configured by an external resistor or when the charging timer reaches the
factory set value.
Using a battery pack with an internal NTC resistor, the Battery Charger IC can monitor the battery temperature
to protect the battery from operating under unsafe thermal conditions.
The Battery Charger IC, as linear charger, is more suitable for applications where the charging source has a
relatively low nominal voltage (~5 V), so that a switching charger is suggested for applications where the
charging source has a relatively high nominal voltage (e.g. ~12 V, see section 2.2.1.7 for specific design-in).
