u-blox LARA-R203 System Integration Manual page 77

2.2.1.8 Guidelines for external battery charging circuit
LARA-R2 series modules do not have an on-board charging circuit. Figure 34 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 STMicroelectronics L6924U 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, set to 10% of the fast-charge current

Fast-charge constant current: the battery is charged with the maximum current, configured by the value of
an external resistor to a value suitable for USB power source (~500 mA)

Constant voltage: when the battery voltage reaches the regulated output voltage (4.2 V), the L6924U 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 to ~15 mA or when the charging timer reaches
the value configured by an external capacitor to ~9800 s.
Using a battery pack with an internal NTC resistor, the L6924U can monitor the battery temperature to protect
the battery from operating under unsafe thermal conditions.
The L6924U, as a 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 2.2.1.9 for specific design-in).
Li-Ion/Li-Polymer
Battery Charger IC
5V
USB
V
IN
Supply
V
INSNS
MODE
ISEL
R1
I
USB
R2
I
AC
R3
I
END
T
PRG
SD
C1 C2
U1
Figure 34: Li-Ion (or Li-Polymer) battery charging application circuit
Reference Description
Li-Ion (or Li-Polymer) battery pack with 470  NTC
B1
C1, C4 1 µF Capacitor Ceramic X7R 0603 10% 16 V
C2, C6 10 nF Capacitor Ceramic X7R 0402 10% 16 V
C3 1 nF Capacitor Ceramic X7R 0402 10% 50 V
C5
330 µF Capacitor Tantalum D_SIZE 6.3 V 45 m
C7 100 nF Capacitor Ceramic X7R 0402 10% 16 V
C8 68 pF Capacitor Ceramic C0G 0402 5% 50 V
C9 15 pF Capacitor Ceramic C0G 0402 5% 25 V
C10 8.2 pF Capacitor Ceramic C0G 0402 5% 50 V
D1, D2 Low Capacitance ESD Protection
R1, R2
24 k Resistor 0402 5% 0.1 W
R3
3.3 k Resistor 0402 5% 0.1 W
R4
1.0 k Resistor 0402 5% 0.1 W
U1
Single Cell Li-Ion (or Li-Polymer) Battery Charger IC
for USB port and AC Adapter
Table 26: Suggested components for a Li-Ion (or Li-Polymer) battery charging application circuit
UBX-16010573 - R12
V
OUT
V
OSNS
V
REF
C3 C4
R4
TH
GND
D1 D2
LARA-R2 series - System Integration Manual
Li-Ion/Li-Pol
Battery Pack
+
θ
C5 C6 C7 C8 C9
B1
Part Number - Manufacturer
Various manufacturer
GRM188R71C105KA12 - Murata
GRM155R71C103KA01 - Murata
GRM155R71H102KA01 - Murata
T520D337M006ATE045 - KEMET
GRM155R61A104KA01 - Murata
GRM1555C1H680JA01 - Murata
GRM1555C1E150JA01 - Murata
GRM1555C1H8R2DZ01 - Murata
CG0402MLE-18G - Bourns
RC0402JR-0724KL - Yageo Phycomp
RC0402JR-073K3L - Yageo Phycomp
RC0402JR-071K0L - Yageo Phycomp
L6924U - STMicroelectronics
LARA-R2 series
VCC
51
52 VCC
VCC
53
C10
GND
Design-in
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