Quectel SC20-WL Hardware Design page 37

system will switch to CC mode. The maximum charging current is 1.44A when adapter is used for
battery charging; and the maximum charging current is 450mA while USB charging.

Constant voltage mode (CV mode): When the battery voltage reaches the final value 4.2V, the
system will switch to CV mode and the charging current will decrease gradually. When the battery
level reaches 100%, the charging is completed.
SC20-WL module supports battery temperature detection in the condition that the battery integrates a
thermistor (47K 1% NTC thermistor with B-constant of 4050K by default; SDNT1608X473F4050FTF of
SUNLORD is recommended) and the thermistor is connected to VBAT_THERM pin. The default battery
temperature range is from -3.0° C~48.5° C. If VBAT_THERM pin is not connected, there will be
malfunctions such as battery charging failure, battery level display error, etc.
A reference design for battery charging circuit is shown as below.
VBAT
NTC
GND
Battery
Figure 12: Reference Design for Battery Charging Circuit
Mobile devices such as mobile phones and handheld POS systems are powered by batteries. When
different batteries are utilized, the charging and discharging curve has to be modified correspondingly so
as to achieve the best effect.
If thermistor is not available in the battery, or adapter is utilized for powering module, then there is only a
need for VBAT and GND connection. In this case, the system may mistakenly judge that the battery
temperature is abnormal, which will cause battery charging failure. In order to avoid this, VBAT_THERM
should be connected to GND with a 47KΩ resistor. If VBAT_THERM is unconnected, the system will be
unable to detect the battery, making battery cannot be charged.
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-WL_Hardware_Design
1
2
3
D1 D2
ESD ESD
Smart Wi-Fi Module Series
SC20-WL Hardware Design
Adapter or USB
R1
0R
C1 C2
100uF 1uF
USB_VBUS
VBAT
VBAT_SNS
VBAT_THERM
GND
Module
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