Charging - Siemens SXG 75 Service Repair Documentation

GSM in which the RF PA current approaches 2A for full power transmit. Under these conditions the
total voltage drop from cell to PA is in the order of 250mV.
With a calibrated cell at 25C the primary shutdown point is intended to occur when sufficient
capacity remains to allow a 3 minute call at high power which is deemed to be a supply current of
350mA. The requirement is for 1 minute, hence 3 minutes is intended to allow some margin for cell
aging and other effects.

9.3 Charging

All the important functions for the power supply of the phone are carried out by the PM6650 power
management IC from Qualcomm. The POWER-pin of the I/O-Connector is for charging the battery
with an external power supply.
The following restrictions must be observed:
• The phone cannot be operated without battery inserted.
• The phone will be damaged if the battery is inserted with wrong polarity (the mechanics
of the phone prevent the battery from being put in the wrong way round. The electric system
assumes that the battery has been inserted correctly. This must be ensured via suitable
QA measures).
• It is inadvisable to remove the battery whilst the phone is connected to the charger unit
however this action would not be expected to damage the phone.
If starting with a deeply discharge battery, charging must take place in three distinct phases. It is
important during charging that the maximum battery terminal voltage does not exceed 4,2 V ± 50
mV.
Trickle charging with a current below 100mA is only necessary when the battery voltage is less than
3.0 V.
The trickle charge current is set to 80mA.
The second phase is termed fast or constant current charging. The current for standard fast
charging can be 950 mA max which is set by the maximum capability of the charger unit. The
current limit of the PM6650 is set to 1.2A to ensure that the charger voltage folds back thus reducing
the pass transistor dissipation.
Fast charging terminates when the battery terminal voltage reaches 4.2V measured by interrogation
of the battery gas gauge. At the end of fast charging the battery will be charged to approximately
80% of its charge capacity.
The final phase of charging is pulsed. During pulse charging the current pulses are again set by the
maximum current capability of the charger unit. The PM6650 current limit is again set to 1.2A to
ensure charger voltage foldback thus minimising pass transistor dissipation. A constant on period of
250 ms is used and the terminal voltage of the battery is not permitted to exceed 4.375V during the
on period of the pulse. The off time of the pulse is 125 ms. Once pulse charging is determined to be
finished a period of maintenance charging commences in which the timing is 125ms on and 500 ms
off. Finally the battery charging is suspended and charging is considered to be completed .
Technical Documentation
TD_Repair_L3_SXG75_R1.0.pdf
Company Confidential
2006©BenQ
Release 1.0
01/2006
Page 44 of 73