MeiG Smart product technical information
SLM758
Hardware Design Guide
Page 55
4.11. Charging Interface
The SLM758 module integrates a 2A charging solution. The charging related content of this
manual is only described by the internal charging scheme. The MSM8953 platform uses the
Qualcomm PMI8952 internal integrated charging chip by default. The chip is in switching
mode and has high efficiency. It integrates a 15-bit battery voltage detection ADC and a 15-bit
current detection ADC. The charging current can be up to 2A.
Figure 4.28: Charging diagram
4.11.1. Charging Detection
When the VBUS pin voltage is higher than 4.0V, a hardware interrupt will be generated
inside the module. The software determines whether the charger is inserted or the USB data
cable is inserted by judging the status of USB_DP/USB_DM.
4.11.2. Charge Control
The SLM758 module can charge the over-discharged battery. The charging process includes
trickle charge, pre-charge, constant current, and constant-voltage charge. When the VBAT
voltage is lower than 3.4V, the module is pre-charged; when VBAT is between 3.4V and 4.2V,
it is charged by the constant current plus constant voltage method optimized for the lithium
battery. At present, the software's charge cut-off voltage is 4.2V, and the back-off voltage is
4.05V.
4.11.3. BAT_CON_TEM
The SLM758 module has battery temperature detection and can be implemented by
BAT_THERM (149PIN). This requires the internal integration of a 10KΩ thermistor (negative
temperature coefficient) inside the battery to connect the thermistor to the BAT_THERM pin.
During the charging process, the software reads the voltage of the BAT_THERM pin to
determine if the battery temperature is too high. If the temperature is too high or too low, the
battery will stop charging immediately to prevent battery damage. The battery charging
connection diagram is shown below:
