EGS5 Hardware Interface Description
3.5 Charging Control
75
EGS5_HD_v02.004
Page 43 of 123
2012-02-09
Confidential / Released
3.5.3
Battery Pack Requirements
The charging algorithm has been optimized for rechargeable Lithium batteries that meet the
characteristics listed below and in
. It is recommended that the battery pack you want
to integrate into your EGS5 application is compliant with these specifications. This ensures re-
liable 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:
10k
+5% @ 25°C, B
25/85
=
3423K to B
=3435K ± 3% (alternatively acceptable:
10k
+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 (pro-
tection 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 EGS5 module, a built-in measuring circuit constantly monitors the supply voltage.
In the event of undervoltage, it causes EGS5 to power down. Undervoltage thresholds are
specific to the battery pack and must be evaluated for the intended model. When you eval-
uate undervoltage thresholds, consider both the current consumption of EGS5
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 150m
, even in extreme conditions at low temperature. The
battery cell must be insensitive to rupture, fire and gassing under extreme conditions of tem-
perature 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 con-
formity.
shows the circuit diagram of a typical battery pack design that includes the protection
elements described above.
Figure 9:
Battery pack circuit diagram
