Specifications

LEON-G100/G200 - System Integration Manual
GSM.G1-HW-09002-C Preliminary System description
Page 25 of 75
Figure 11: Valid area for the charger V-I output characteristics using a 1100 mAh Li-Ion Battery
1.5.4 Voltage Backup Power (V_BCKP)
The V_BCKP pin connects the Real Time Clock (RTC) supply, which is internally generated by a linear regulator
integrated in the module chipset. The output of this linear regulator is enabled when the main voltage supply
providing the module through VCC is within the valid operating range or if the module is switched-off.
The RTC provides the time reference (date and time) of the module, also in power-off mode, since the RTC runs
when the V_BCKP voltage is within its valid range (specified in LEON-G100/G200 Data Sheet [1]). The RTC block
is able to provide programmable alarm functions by means of the internal 32.768 kHz clock.
The RTC block has very low power consumption, but this is highly temperature dependent. For example at 25°C
and a V_BCKP voltage of 2.0 V the power consumption is approximately 2 µA, whereas at 85°C and an equal
voltage the power consumption increases to 5 µA.
The RTC can be supplied from an external back battery through the V_BCKP, when the main voltage supply is
not provided to the module through VCC. This lets the time reference (date and time) run even when the main
supply is not provided to the module. The module cannot switch on if a valid voltage is not present on VCC even
when RTC is supplied through V_BCKP (meaning that VCC is mandatory to switch-on the module).
If V_BCKP is left unconnected and the main voltage supply of the module is removed from VCC, the RTC be
supplied from the 1 µF buffer capacitor mounted inside the module. However, this capacitor is not able to
provide a long buffering time: within 0.5 seconds the voltage on V_BCKP will go below the valid range (1 V
min).
V_BCKP can be left unconnected if RTC is not required when VCC supply is removed.
If RTC is required to run for a time interval of T [seconds] at 25°C when VCC supply is removed, place a capacitor
with a nominal capacitance of C [µF] at the V_BCKP pin. Chose the capacitor with the following formula:
C [µF] = ( Current_Consumption [µA] x T [seconds] ) / Voltage_Drop [V] = 2 x T [seconds]
The current consumption of the RTC is around 2 µA at 25°C, and the voltage drop is equal to 1 V (from the
V_BCKP typical value of 2.0 V to the valid range minimum limit of 1.0 V).
For example, a 100 µF capacitor (such as the Murata GRM43SR60J107M) can be placed at the V_BCKP to
provide a long buffering time. This capacitor will hold V_BCKP voltage within its valid range for around 50
seconds at 25°C, after the VCC supply is removed. If a very long buffering time is required, a 70 mF super-
capacitor (e.g. Seiko Instruments XH414H-IV01E) can be placed at V_BCKP, with a 4.7 k series resistor to hold
Charger specification using
a 1100 mAh Li-Ion Battery
16
15.0
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
400
0
mA
V
5.6
1200
800700600500300200100 900 1000 1100 1300
Charger specification using
a 1100 mAh Li-Ion Battery
16
15.0
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
400
0
mA
V
5.6
1200
800700600500300200100 900 1000 1100 1300