Ublox MPCI-L2 Series System Integration Manual page 78
Lte/dc-hspa+/egprs modules
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- System integration manual (141 pages) ,
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2.2.1.7
Guidelines for external battery charging circuit
TOBY-L2 modules do not have an on-board charging circuit. Figure 37 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
TOBY-L2 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.
Alternatively the L6924U, providing input voltage range up to 12 V, can charge from an AC wall adapter. When
a current-limited adapter is used, it can operate in quasi-pulse mode, reducing power dissipation.
Li-Ion/Li-Polymer
Battery Charger IC
5V0
USB
V
V
IN
OUT
Supply
V
V
INSNS
OSNS
MODE
V
REF
ISEL
R1
I
USB
R2
I
TH
AC
R3
I
END
T
PRG
SD
GND
C1
C2
U1
Figure 37: 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% 50 V
C10
8.2 pF Capacitor Ceramic C0G 0402 5% 50 V
D1
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
Table 19: Suggested components for Li-Ion (or Li-Polymer) battery charging application circuit
UBX-13004618 - R07
TOBY-L2 and MPCI-L2 series - System Integration Manual
Li-Ion/Li-Pol
Battery Pack
C3
R4
C4
θ
B1
D1
Advance Information
TOBY-L2 series
VCC
70
VCC
71
VCC
72
+
C5
C6
C7
C8
C9
C10
GND
Part Number - Manufacturer
Various manufacturer
GRM188R71C105KA12 - Murata
GRM155R71C103KA01 - Murata
GRM155R71H102KA01 - Murata
T520D337M006ATE045 - KEMET
GRM155R61A104KA01 - Murata
GRM1555C1H680JA01 - Murata
GRM1555C1H150JA01 - Murata
GRM1555C1H8R2DZ01 - Murata
USB0002RP or USB0002DP - AVX
RC0402JR-0724KL - Yageo Phycomp
RC0402JR-073K3L - Yageo Phycomp
RC0402JR-071K0L - Yageo Phycomp
L6924U - STMicroelectronics
Design-in
Page 78 of 158
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