Backup Battery - Nokia n81 Service Manual

RM-179; RM-223
System Module and User Interface
The battery temperature is estimated by measuring separate battery temperature NTC via the BTEMP line.
This is located on the main PWB, at the place where the phone temperature is closest to the battery
temperature.
Battery connector
The battery connector is a blade connector. It has three blades;
• BSI (Battery size indicator)
• GND (Ground)
• VBAT (Battery voltage)
The BSI line is used to recognize the battery capacity by a battery internal pull down resistor.
Figure 54 Battery connector
Charging
This phone is charged through the smaller Nokia standard interface (2.0 mm plug). The wider standard
charger (3.5 mm) can be used together with the CA-44 charger adapter.
Figure 55 Small (right) and wide (left) charger plug
Charging is controlled by energy management, and external components are needed to protect the baseband
module against EMC, reverse polarity and transient frequency deviation.

Backup battery

When the main battery is not attached EM ASIC (N2200) goes in backup mode using back-up battery that
supplies voltage to RTC in EM ASIC (N2200).
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