> 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 10. It is recommended that the battery pack you want to integrate into your TC65 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 capacity higher than 500 mAh.

> • | 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 start if no NTC is present.

> • | Ensure that the pack incorporates a protection circuit capable of detecting overvoltage (protection against overcharging), undervoltage (protection against deep discharging) and overcurrent. Due to the discharge current profile typical of GSM applications, the circuit must be insensitive to pulsed current.

> • | On the TC65 module, a built-in measuring circuit constantly monitors the supply voltage. In the event of undervoltage, it causes TC65 to power down. Undervoltage thresholds are specific to the battery pack and must be evaluated for the intended model. When you evaluate undervoltage thresholds, consider both the current consumption of TC65 and of the application circuit.

> • | The internal resistance of the battery and the protection should be as low as possible. It is recommended not to exceed 150mÙ, even in extreme conditions at low temperature. The battery cell must be insensitive to rupture, fire and gassing under extreme conditions of temperature and charging (voltage, current).

> • | The battery pack must be protected from reverse pole connection. For example, the casing should be designed to prevent the user from mounting the battery in reverse orientation.

> • | It is recommended that the battery pack be approved to satisfy the requirements of CE conformity.

> Figure 10 shows the circuit diagram of a typical battery pack design that includes the protection elements described above.
> Figure 10: Battery pack circuit diagram

> Table 10: | Specifications of battery packs suitable for use with TC65

> Battery type | Rechargeable Lithium Ion or Lithium Polymer battery
> Nominal voltage | 3.6V / 3.7V
> Capacity | Recommended: 1000mAh to 1200mAh Minimum: 500mAh
> NTC | 10kΩ ± 5% @ 25°C approx. 5kΩ @ 45°C approx. 26.2kΩ @ 0°C B value range: B (25/85)=3423K to B =3435K ± 3%
> Overcharge detection voltage | 4.325 ± 0.025V
> Overdischarge detection voltage | 2.4V
> Overdischarge release voltage | 2.6V
> Overcurrent detection | 3 ± 0.5A
> Overcurrent detection delay time | 4 ~ 16ms
> Short detection delay time | 50µs
> Internal resistance | <130mΩ Note: A maximum internal resistance of 150m Ω should not be exceeded even after 500 cycles and under extreme conditions.