User's Manual

page 29/51
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User Manual 2012/06/28
Figure 22: internal charging of backup battery or 10uF capacitor
The value of resistor R depends on the charging current value of the backup battery manufacturer.
3.9.4 Capacitor backup battery technology
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SAGEMCOM strongly recommends using Supercap technology.
These kinds of backup battery have not the drawbacks of the Lithium Ion rechargeable battery.
As there are only capacitors:
• The maximum discharge current is generally bigger,
• There is no problem of over-discharge: the capacitor is able to recover its full charge even if its voltage
has previously fallen to 0V.
• There is no need to regulate the charging current.
Moreover, this kind of battery is available in the same kind of package than the Lithium Ion cell and fully
compatible on a mechanical point of view. The only disadvantage is that the capacity of this kind of battery is
significantly smaller than Manganese Silicon Lithium Ion battery. But for this kind of use (supply internal RTC
when the main battery is removed), the capacity is generally enough.
VBACKUP
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10µF capacitor
VBACKUP
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R
Backup battery