Quectel SC20 Series Hardware Design page 42

Trickle charging: There are two steps in this mode. When the battery voltage is below 2.8 V, a

90 mA trickle charging current is applied to the battery. When the battery voltage is charged up and is
between 2.8 V and 3.2 V, the charging current can be set to 450 mA maximally.
Constant current mode (CC mode): When the battery is increased to between 3.2 V and 4.2 V, the

system will switch to CC mode. The maximum charging current is 1.44 A when adapter is used for
battery charging; and the maximum charging current is 450 mA during USB charging.
Constant voltage mode (CV mode): When the battery voltage reaches the final value 4.2 V, the

system will switch to CV mode and the charging current will decrease gradually. When the battery
level reaches 100 %, the charging is completed.
The module supports battery temperature detection in the condition that the battery integrates a
thermistor (47 kΩ 1 % NTC thermistor with B-constant of 4050 K by default; SDNT1608X473F4050FTF of
SUNLORD is recommended) and the thermistor is connected to VBAT_THERM pin. If VBAT_THERM pin
is not connected, there will be malfunctions such as battery charging failure, battery level display error,
etc. The default battery temperature range is -3.0 °C to 48.5 °C.
A reference design for battery charging circuit is shown as below.
Mobile devices such as mobile phones and handheld POS systems are powered by batteries. When
different batteries are utilized, the charging and discharging curve must be modified correspondingly to
achieve the best effect.
If the thermistor is not available in the battery, or an adapter is utilized for powering module, you must
connect VBAT_THERM to GND via a 47 kΩ resistor. Otherwise, the system may mistakenly judge that
the battery temperature is abnormal, and therefore cause battery charging failure.
VBAT_SNS pin must be connected. Otherwise, the module will have abnormalities in voltage detection,
as well as associated power-on/off and battery charging/discharging issues.
SC20_Series_Hardware_Design
Figure 12: Reference Design for Battery Charging Circuit
Smart Module Series
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