Battery/Charging; Battery; Phone Shutdown Due To Low Battery - Siemens SXG 75 Service Repair Documentation

9 Battery/Charging

9.1 Battery

The battery is a high capacity LiIon - battery pack nominally rated at 4.2 V open circuit terminal
voltage and about 1000 mAh minimal capacity. The battery pack has in-built electrical protection
circuitry and contains a BQ27000 fuel gauge monitor from Texas Instruments. The fuel gauge signal
is a 1-wire HDQ interface. See Section 13 for details of the fuel gauge interface.
The battery pack has the following parameters:
The BQ27000 is programmed with the following parameters.
(Note: These parameters are subject to change, consequently if critical to work being undertaken it
will be advisable to check these values)
• Initial LMD 914 mAh
• EDVF Threshold 3384 mV
• EDVI threshold 3592 mV
• Initial standby load 4.28 mA
• Digital filter threshold 4.9 µV
• Self discharge rate 0.11 % per day
• Taper current 76 mA
• Pack configuration 60 hex
• Initial max load 274.2 mA
• Dsg rate comp gain 9.8 %LMD/C-rate
• Dsg rate comp threshold 2 mAh Code (0~3)
• Temperature comp gain 1.46 %LMD/ °C
• Temp comp offset 14 °C

9.2 Phone shutdown due to low battery

Shutdown of the handset takes place in two stages. Both stages of shutdown are controlled in
software depending on parameters read from the battery fuel gauge. The stages are:
• Stage 1: This occurs either when the fuel gauge reports 3.400V if the fuel gauge is reporting that it
is uncalibrated, or when the fuel gauge reports that the first capacity limit has been passed by
setting the EDV1 flag to 1.
• Stage 2: This occurs when the battery fuel gauge reports that the cell voltage has fallen below
3.200V. (Note that the fuel gauge EDVF flag is not used in current software)
Fuel gauge readings cannot be synchronised with GSM RF bursts so to avoid fluctuations in
readings, the fuel gauge effectively applies a RC filter with a cut off frequency of 159Hz (time
constant 6.3ms) to the readings to generate a filtered value which is reported via the digital
interface.
The fuel gauge reports cell voltage not battery terminal voltage. Hence under high load conditions
an error will exist if the cell voltage is assumed to be the handset battery terminal voltage or
particularly the GSM PA voltage. The difference is greatest under high current supply conditions and
worst case is full power
Technical Documentation
TD_Repair_L3_SXG75_R1.0.pdf
Company Confidential
2006©BenQ
Release 1.0
01/2006
Page 43 of 73