MeiG_SLM550_Hardware Design Manual
MeiG Smart Technology Co., Ltd
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charging current gradually decreases, the charging current drops to about 100mA, and the charging is
stopped.
Figure 33 Charging diagram
4.10.1 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.
4.10.2 Charge Control
The SLM550 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.
4.10.3 BAT_CON_TEM
The SLM550 module has battery temperature detection and can be implemented by BAT_THERM
(134PIN). This requires the internal integration of a 47KΩ 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:
