SIM802 Hardware Design
Figure 11: Battery charger and pack
The function of detecting the temperature of battery should be supported by the software in the
module. It’s a customization function. The R
TEMP
is a NTC thermistor. We recommend to use
NCP15XH103F03RC from MURATA. The impedance of the NTC thermistor is 10Kohm in 25 .
℃
Please refer to the fore figure for the reference circuit.
3.5.1 Battery pack characteristics
SIM802 has optimized the charging algorithm for the Li-Ion battery that meets the characteristics
listed below. To use SIM802’s charging algorithm properly, it is recommended that the battery
pack you integrated into your application is compliant with these specifications. The battery pack
compliant with these specifications is also important for the AT command “AT+CBC” to monitor
the voltage of battery, or the “AT+CBC” may return incorrect battery capacity values.
z
The maximum charging voltage of the Li-Ion battery pack is 4.2V and the recommended
capacity is 580mAh. If the Battery packs with a capacity more than 580 mAh, it will cost
more time for charging.
z
The pack should have a protection circuit to avoid overcharging, deep discharging and
over-current. This circuit should be insensitive to pulsed current.
z
On the SIM802, the build-in circuit of SIM802’s power management chipset monitors the
supply voltage constantly. Once the Under-voltage is detected, the SIM802 will be power
down automatically. Under-voltage thresholds are specific to the battery pack.
z
The internal resistance of the battery and the protection circuit should be as low as possible.
It is recommended not to exceed
200m
Ω
.
z
The battery pack must be protected from reverse pole connection.
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