User's Manual

SARA-R4 series - System Integration Manual
UBX-16029218 - R03 Design-in
Page 36 of 94
C2
GND
C5
SARA-R4 series
52
VCC
53
VCC
51
VCC
C1
3V8
C3 C4
Figure 13: Suggested schematic for the VCC bypass capacitors to reduce ripple / noise on supply voltage profile
Reference
Description
Part Number - Manufacturer
C1
68 pF Capacitor Ceramic C0G 0402 5% 50 V
GRM1555C1H680JA01 - Murata
C2
15 pF Capacitor Ceramic C0G 0402 5% 50 V
GRM1555C1H150JA01 - Murata
C3
10 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R71C103KA01 - Murata
C4
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R71C104KA01 - Murata
C5
10 µF Capacitor Ceramic X5R 0603 20% 6.3 V
GRM188R60J106ME47 - Murata
Table 11: Suggested components to reduce ripple / noise on VCC
The necessity of each part depends on the specific design, but it is recommended to provide all the bypass
capacitors described in Figure 13 / Table 11 if the application device integrates an internal antenna.
ESD sensitivity rating of the VCC supply pins is 1 kV (HBM according to JESD22-A114). Higher protection
level can be required if the line is externally accessible on the application board, e.g. if accessible battery
connector is directly connected to the supply pins. Higher protection level can be achieved by mounting
an ESD protection (e.g. EPCOS CA05P4S14THSG varistor) close to accessible point.
2.2.1.7 Guidelines for external battery charging circuit
SARA-R4 series modules do not have an on-board charging circuit. Figure 14 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 that, from a USB power source
(5.0 V typ.), charges as a linear charger 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 the following section 2.2.1.8 for specific
design-in).