3. TECHNICAL BRIEF
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3.15. USB charging circuit
The USB charging circuit is a fully integrated USB VBUS voltage single-cell Li-ion battery charger
circuit.
The charger uses a CC/CV charge profile required by Li-ion batteries. CC charging current and End of
charging current is programmable I
REF
& I
MIN
resistors.
I
REF
resistor between this pin and the GND pin to set the charge current limit determined by the
following equation:
I
CC
= 12089/39K = 310mA
The End Of Charging current is set by IMIN That can be programmed by the as following equation:
I
EOC
= 11000/220K = 50mA
Charging indicator LED LD100 controlled by S-GOLD2’s GPIO that is CHG_LED_CTRL. When
TA(Travel Adaptor) is plugged in to 18pin MMI connector, SM-POWER detect charger voltage then
inform charger detecting to S-GOLD2. S-GOLD2 maintain low level of CHG_LED_CTRL until get
EOC(End Of Charging) message from SM-POWER. The LD100 controlled by S-GOLD2 both power
off and power on case. When USB cable is connected via MMI connector, indicator LED is controlled
same mechanism with TA inserted case. USB charging EOC is not indicated when the terminal is in off
status. LED just indicates charging status even though USB charging process reached EOC because
S_GOLD2 is in off status.
Figure 27 USB charging circuit
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