Quectel Smart LTE Module Series Hardware Design page 47

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. If VBAT_THERM pin
is not connected, there will be malfunctions such as boot error, battery charging failure, battery level
display error, etc.
A reference design for battery charging circuit is shown as below.
VBAT
NTC
GND
Battery
Figure 10: Reference Design for Battery Charging Circuit
SC650T offers a fuel gauge algorithm that is able to accurately estimate the battery's state by current and
voltage monitor techniques. Using precise measurements of battery voltage, current, and temperature,
the fuel gauge provides a dependable state of charge estimate throughout the entire life of the battery and
across a broad range of operating conditions. It effectively protects the battery from over-discharging, and
also allows users to estimate the battery life based on the battery level so as to timely save important data
before completely power-down.
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 the module, then there is only
a need for VBAT and GND connection. In this case, the system may be unable to detect the battery,
which will cause power-on failure. In order to avoid this, VBAT_THERM should be connected to GND with
a 47KΩ resistor. VBAT_SNS, BAT_PLUS and BAT_MINUS must be connected, otherwise there may be
abnormalities in use of the module. Among them, BAT_PLUS and BAT_MINUS are used for battery level
detection, and they should be routed as differential pair to ensure accuracy.
SC650T_Hardware_Design
R2
NC
R3
NC
R1
0805
0R
D2 C1
D1
ESD ESD 100uF
Smart LTE Module Series
SC650T Hardware Design
Adapter or USB
USB _VBUS
CS _PLUS
CS _MINUS
VBAT
BAT_PLUS
VBAT_SNS
BAT_THERM
BAT _ MINUS
GND
C2 C3
Module
1 uF
33 pF
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