LENA-R8 series - System integration manual
UBX-22015376 - R02
Design-in
Page 39 of 116
C1-Public
2.2.1.5
Guidelines for VCC supply circuit design using a primary battery
The characteristics of a primary (non-rechargeable) battery connected to the
VCC
pins should meet
the following prerequisites to comply with the module’s
VCC
•
Maximum pulse and DC discharge current
: the non-rechargeable battery with its related output
circuit connected to the
VCC
pins must be capable of delivering a pulse current as the maximum
peak current consumption during a Tx burst at the maximum Tx power specified in the LENA-R8
series data sheet
, and must be capable of extensively delivering a DC current as the maximum
average current consumption specified in the LENA-R8 series data sheet
. The maximum
discharge current is not always reported in the data sheets of batteries, but the max DC discharge
current is typically almost equal to the battery capacity in amp-hours divided by 1 hour.
•
DC series resistance
: the non-rechargeable battery with its output circuit must be capable of
avoiding a
VCC
voltage drop below the operating range summarized in
bursts.
2.2.1.6
Guidelines for external battery charging circuit
LENA-R8 series modules do not have an on-board charging circuit.
a battery charger design, suitable for applications powered with a Li-ion (or Li-Polymer) battery.
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
for specific design-in).
C5
C8
GND
C7
C6
C9
LENA-R8 series
52
VCC
53
VCC
51
VCC
+
USB
supply
C3
R4
θ
U1
I
USB
I
AC
I
END
T
PRG
SD
V
IN
V
INSNS
MODE
ISEL
C2
C1
5V
TH
GND
V
OUT
V
OSNS
V
REF
R1
R2
R3
Li-Ion/Li-Pol
Battery Pack
D1
B1
C4
Li-Ion/Li-Polymer
battery charger IC
D2
C10
Figure 22: Li-ion (or Li-Polymer) battery charging application circuit
