Siemens S45 Service Manual page 17

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 10kΩ 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. The NTC for the ambient temperature will be in the phone on the main
component group.
Recognition of the Battery Type
The battery code will be an resistor with a resistance of 8.2kΩ up to 56kΩ depending
on the manufacturer:
8.2kΩ corresponds to Panasonic
15kΩ corresponds to NEC
27kΩ corresponds to Sanyo
56kΩ not allocated
If no resistance is recognised, then the battery will not be charged.
Charging Characteristic of Lithium-Ion Cells
Li-Ion 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 approx. 600mA, minimum about 100mA. The battery
voltage may not exceeds 4.2V ±50mV. The temperature range in which charging of the
phone may be started ranges from 5...40°C, and the temperature at which charging
takes place is from 0...45°C. Outside this range no charging takes place, the battery only
supplies current. Above 50°C the battery no longer supplies any current.
Trickle Charging
The power supply ASIC is able to charge the battery at voltages below 3.2V without any
support from the charge SW. The current will by measured by a shunt resistance and
linearly regulated inside the ASIC by means of the external FET driven in it´s active
region of the transfer characteristic as a typical linear pass element. 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 3.75V. The maximum trickle time is 1 hour.
Matching up
In order to guarantee a correct working of the charge control, the measurement
hardware in the phone must be matched up. The matching up is done by means of a
self-test.
Restrictions
• A battery which has completely run down can not be re-charged quickly because
the battery voltage is less than 3.0V and the logics which implements the charge
control cannot be operated at this low voltage level. In this case the battery is
recharged via trickle-charging. However, the charging symbol cannot be shown in
the display because at this time logic supply voltages are not operating. The
charging time for this trickle-charging (until the battery can be fast-charged from
then on) is in the range of 1 hours. If, within this time, a voltage of 3.2V is
exceeded, then the ASIC switches on the mobile and charging continues in the
Charge-Only Mode. In some circumstances it can happen that after trickle-
charging and the usually initiated switch-on procedure of the mobile, the supply