TOBY-L1 and MPCI-L1 series - System Integration Manual
UBX-13001482 - R04
Advance Information
Design-in
Page 42 of 90
C2
GND
C3
C4
TOBY-L1 series
71
VCC
72
VCC
70
VCC
C1
3V8
C2
GND
C3
C4
MPCI-L1 series
C1
3V3
24
3.3Vaux
39
3.3Vaux
2
3.3Vaux
41
3.3Vaux
52
3.3Vaux
Figure 22: Suggested schematic for the VCC / 3.3Vaux 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
Table 13: Suggested components to reduce ripple / noise on VCC / 3.3Vaux
ESD sensitivity rating of the
VCC / 3.3Vaux
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 supply pins. Higher protection level can be achieved
by mounting an ESD protection (e.g. EPCOS CA05P4S14THSG varistor array) close to accessible point.
2.2.1.7
Guidelines for external battery charging circuit
TOBY-L1 series modules do not have an on-board charging circuit. Figure 23 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-L1 series 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.
