User's Manual
TOBY-R2 series - System Integration Manual
UBX-16010572 - R04 Design-in
Page 75 of 147
2.2.1.8 Guidelines for external battery charging circuit
TOBY-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 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).
C5 C8C7C6 C9
GND
TOBY-R2 series
71
VCC
72
VCC
70
VCC
+
USB
Supply
C3
R4
θ
U1
IUSB
IAC
IEND
TPRG
SD
VIN
VINSNS
MODE
ISEL
C2C1
5V0
TH
GND
VOUT
VOSNS
VREF
R1
R2
R3
Li-Ion/Li-Pol
Battery Pack
D1
B1
C4
Li-Ion/Li-Polymer
Battery Charger IC
D2
Figure 34: Li-Ion (or Li-Polymer) battery charging application circuit
Reference
Description
Part Number - Manufacturer
B1
Li-Ion (or Li-Polymer) battery pack with 470 NTC
Various manufacturer
C1, C4
1 µF Capacitor Ceramic X7R 0603 10% 16 V
GRM188R71C105KA12 - Murata
C2, C6
10 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R71C103KA01 - Murata
C3
1 nF Capacitor Ceramic X7R 0402 10% 50 V
GRM155R71H102KA01 - Murata
C5
330 µF Capacitor Tantalum D_SIZE 6.3 V 45 m
T520D337M006ATE045 - KEMET
C7
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R61A104KA01 - Murata
C8
68 pF Capacitor Ceramic C0G 0402 5% 50 V
GRM1555C1H680JA01 - Murata
C9
15 pF Capacitor Ceramic C0G 0402 5% 50 V
GRM1555C1H150JA01 - Murata
D1, D2
Low Capacitance ESD Protection
CG0402MLE-18G - Bourns
R1, R2
24 k Resistor 0402 5% 0.1 W
RC0402JR-0724KL - Yageo Phycomp
R3
3.3 k Resistor 0402 5% 0.1 W
RC0402JR-073K3L - Yageo Phycomp
R4
1.0 k Resistor 0402 5% 0.1 W
RC0402JR-071K0L - Yageo Phycomp
U1
Single Cell Li-Ion (or Li-Polymer) Battery Charger IC
L6924U - STMicroelectronics
Table 25: Suggested components for Li-Ion (or Li-Polymer) battery charging application circuit