Siemens C75 Service Repair Documentation page 26

Company Confidential
Copyright 2005© Siemens AG
For controlling the charging process it is necessary to measure the ambient (phone)
temperature and the battery voltage. The temperature sensor will be an NTC resistor with a
nominal resistance of 22kΩ at 25°C. The determination of the temperature is achieved via a
voltage measurement on a voltage divider in which one component is the NTC. Charging is
ongoing as long the temperature is within the range +5°C to 45°C. The maximal charge time
will be 2 hours (I
max
7.1.2.2 Measurement of Battery voltage, Battery Type and Ambient Temperature
he voltage equivalent of the temperature and battery code on the voltage separator will be
T
calculated as the difference against a reference voltage of the S-GOLDlite. Inside the S-
GOLDlite are some analog to digital converters. These are used to measure the battery
voltage, battery code resistor and the ambient temperature.
7.1.2.3 Timing of the Battery Voltage Measurement
Unless the battery is being charged, the measurement shall be made in the TX time slot.
During charging it will be done after the TX time slot.
7.1.2.4 Recognition of the Battery Type
The different batteries will be encoded by different resistors within the battery pack itself.
7.1.2.5 Charging Characteristic of Lithium-Ion Cells
LiIon batteries are charged with a U/I characteristic, i.e. the charging current is regulated in
relation to the battery voltage until a minimal charging current has been achieved. The
maximum charging current is given by the connected charger. The battery voltage may not
exceed 4.2V ±50mV average. During the charging pulse current the voltage may reach 4.3V.
The temperature range in which charging of the phone may be performed is in the ranges
from 0...50°C. Outside this range no charging takes place, the battery only supplies current.
7.1.2.6 Trickle Charging
The ASIC is able to charge the battery at voltages below 3.2V without any support from the
charge SW. The current will by measured indirectly via the voltage drop over a shunt resistor
and linearly regulated inside the ASIC by means of the external FET. The current level during
trickle charge for voltages <2.8V is in a range of 20-50mA and in a range of 50-100mA for
voltages up to 3.2V. To limit the power dissipation of the dual charge FET the trickle charging
is stopped in case the output voltage of the charger exceeds 10 Volt. The maximum trickle
time is limited to 1 hour. As soon as the battery voltage reaches 3.2 V the ASIC will switch on
the phone automatically and normal charging will be initiated by software.
7.1.2.7 Normal Charging (Fast charge)
For battery voltages above 3.2 Volt and normal ambient temperature between 0 and 50°C the
battery can be charged with a charge current up to 1C. This charging mode is SW controlled
and starts if an accessory (charger) is detected with a supply voltage above 6.4 Volt by the
ASIC ASIC. The level of charge current is only limited by the charger.
Service Repair Documentation
Level 2.5e – C75
=750mA).
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