Integration Manual

SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 47 of 119
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.
• 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 the specific design-in).