Hardware Interface Description - Wireless Data Modules

MC55/56 Hardware Interface Description
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3.5.1 Battery pack characteristics
The charging algorithm has been optimised for a Li-Ion battery pack that meets the
characteristics listed below and in Table 8. It is recommended that the battery pack you want
to integrate into your MC55/56 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 (see [1] for details). Failure to comply with
these specifications might cause AT^SBC to deliver incorrect battery capacity values.
• Li-Ion battery pack specified for a maximum charging voltage of 4.2 V and a capacity of
800 mAh. Battery packs with a capacity down to 600 mAh or more than 800 mAh are
allowed, too.
• 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. Required NTC characteristics are: 10 kΩ +5% @ 25°C, B 25/85 =
3435K +3% (alternatively acceptable: 10 kΩ +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. The circuit must be insensitive to pulsed current.
• On the MC55/56 module, a built-in measuring circuit constantly monitors the supply
voltage. In the event of undervoltage, it causes MC55/56 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
MC55/56 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 150mΩ, 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.
• The battery pack must be approved to satisfy the requirements of CE conformity.
Figure 8 shows the circuit diagram of a typical
battery pack design that includes the protection
elements described above.
to BATT+
to BATT_TEMP
ϑ
to GND
NTC
Protection Circuit
+ -
Figure 8: Battery pack circuit diagram
Battery cell
Polyfuse
MC55/56_hd_v02.06 Page 39 of 105 29.10.2004