User's Manual

TC63 Hardware Interface Description
Strictly confidential / Draft
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TC63_HD_V00.432 Page 36 of 97 11.05.2005
3.5 Charging Control
TC63 integrates a charging management for rechargeable Lithium Ion and Lithium Polymer
batteries. You can skip this chapter if charging is not your concern, or if you are not using the
implemented charging algorithm.
The following sections contain an overview of charging and battery specifications. Please
refer to [4] for greater detail, especially regarding requirements for batteries and chargers,
appropriate charging circuits, recommended batteries and an analysis of operational issues
typical of battery powered GSM/GPRS applications.
3.5.1 Hardware Requirements
TC63 has no on-board charging circuit. To benefit from the implemented charging
management you are required to install a charging circuit within your application according to
the Figure 38.
3.5.2 Software Requirements
Use the command AT^SBC, parameter <current>, to enter the current consumption of the
host application. This information enables the TC63 module to correctly determine the end of
charging and terminate charging automatically when the battery is fully charged. If the
<current> value is inaccurate and the application draws a current higher than the final charge
current, either charging will not be terminated or the battery fails to reach its maximum
voltage. Therefore, the termination condition is defined as: final charge current (50mA) plus
current consumption of the external application. If used the current flowing over the VEXT pin
of the application interface (typically 2.9V) must be added, too.
The parameter <current> is volatile, meaning that the factory default (0mA) is restored each
time the module is powered down or reset. Therefore, for better control of charging, it is
recommended to enter the value every time the module is started.
See [1] for details on AT^SBC.
3.5.3 Battery Pack Requirements
The charging algorithm has been optimized for rechargeable Lithium batteries that meet the
characteristics listed below and in Table 3. It is recommended that the battery pack you want
to integrate into your TC63 application is compliant with these specifications. This ensures
reliable operation, proper charging and, particularly, allows you to monitor the battery
capacity using the AT^SBC command. Failure to comply with these specifications might
cause AT^SBC to deliver incorrect battery capacity values.
• Li-Ion or Lithium Polymer battery pack specified for a maximum charging voltage of 4.2V
and a recommended capacity of 1000 to 1200mAh.
• Since charging and discharging largely depend on the battery temperature, the battery
pack should include an NTC resistor. If the NTC is not inside the battery it must be in
thermal contact with the battery. The NTC resistor must be connected between
BATT_TEMP and GND.
The B value of the NTC should be in the range: 10kΩ +
5% @ 25°C, B
25/85
= 3423K to B
=3435K ± 3% (alternatively acceptable: 10kΩ +
2% @ 25°C, B
25/50
= 3370K +3%). Please
note that the NTC is indispensable for proper charging, i.e. the charging process will not