MB39A125 Datasheet, PDF (28/64 Pages) Fujitsu Component Limited. – DC/DC Converter IC for Charging Li-ion Battery

MB39A125/126
■ CONSTANT CHARGING VOLTAGE AND CURRENT OPERATION
MB39A125/126 is DC/DC converter with the pulse width modulation (PWM) .
MB39A125 is in the output voltage control loop, the Error Amp3 compares internal voltage reference voltage
4.2 V and DC/DC converter output to output the PWM controlled signal.
MB39A126 is in the output voltage control loop, the Error Amp3 compares internal voltage reference voltage
4.2 V/3.15 V and DC/DC converter output to output the PWM controlled signal.
In the charging current control loop, the voltage drop generated at both ends of charging current sense resistor
(RS2) is sensed by +INC1 terminal (pin 13) , −INC1 terminal (pin 12) of Current Amp1, and the signal is output
to OUTC1 terminal (pin 10) , which is amplified by 20 times. Error Amp1 compares the OUTC1 terminal (pin
10) voltage, which is the output of Current Amp1, and +INE1 terminal (pin 9) to output the PWM control signal
and regulates the charging current.
In the AC adapter current control loop, the voltage drop generated at both ends of AC adapter current sense
resistor (RS1) is sensed by +INC2 terminal (pin 24) , −INC2 terminal (pin 1) of Current Amp2, and the signal is
output to OUTC2 terminal (pin 2) , which is amplified by 20 times. Error Amp2 compares OUTC2 terminal (pin
2) voltage, which is output of Current Amp2, and +INE2 terminal (pin 3) voltage and outputs PWM controlled
signal, and it limits the charging current due to the AC adapter current not to exceed the setting value.
The PWM comparator compares the triangular wave to the smallest terminal voltage among the Error AMP1,
Error AMP2 and Error AMP3. And the triangular wave voltage generated by the triangular wave oscillator. When
the triangular wave voltage is smaller than the error amplifier output voltage, the main side output transistor is
turned on.
28