MB3813A Datasheet, PDF (14/22 Pages) Fujitsu Component Limited. – Lithium Ion Battery Charger DC/DC Converter IC (High Precision with Constant-current Function)

MB3813A/MB3833A/MB3843
s FUNCTIONAL DESCRIPTION
1. Switching Regulator Block
(1) Reference voltage circuit (Ref)
The reference voltage circuit uses the voltage supply from the VCC pin (pin 14) to generate a temperature
compensated, stable voltage (=: 2.50 V) for use as the reference voltage for the internal circuits of the IC chip.
It is also possible to supply a reference voltage output of up to 1 mA to external circuits through the VREF pin
(pin 9).
(2) Triangular wave oscillator circuit (OSC)
By connecting the CT pin (pin 13) and RT pin (pin 12) respectively to a capacitance and resistance for timing,
a triangular oscillator waveform can be generated.
The triangular wave is input to the PWM comparator circuits on the IC. At the same time, it can also be supplied
to an external device from the CT terminal.
(3) Error amplifier circuit (Error Amp.1)
The error amplifier circuit is used to detect the output voltage from the switching regulator and produces the
PWM control signal. No external resistance is required at the error amplifier inversion input pin, because the
output voltage setting resistance is connected within the IC. The output voltage settings are defined as:
MB3813A 12.6 V/12.3 V, MB3833A 8.4 V/8.2 V, MB3843 4.2 V/4.1 V, the optimum levels respectively for use
with 3-cell, 2-cell and 1-cell lithium-ion batteries.
Also, by connecting feedback resistance and capacitance between the error amplifier FB pin (pin 6) and -IN
pin (pin 5), it is possible to set the desired level of loop gain to provide stabilized phase compensation to the
system.
The CS pin (pin 11) can be connected to a soft start capacitor to prevent current surges at startup. The soft
start is detected by the error amplifier, which provides a constant soft start time independent of output load.
(4) Current detector amplifier circuit (Current Amp.)
The current detector amplifier provides 25 × amplification of the voltage drop between the two ends of the
output sensor resistor (RS) in the switching regulator, that occurs due to the flow of the charging current. This
voltage drop is compared to the voltage at the Vin2 pin (pin 8) in the next stage error amplifier circuit (Error
Amp.2), and used to control the charging current.
(5) Power supply control circuit (CTL)
An “L” level signal input to the CTL pin (pin 7) places the IC in standby mode. In standby mode, all circuits
other than input detection circuits are switched off.
(6) PWM comparator circuit (PMW Comp.)
This is a voltage-pulse width conversion circuit that controls the output duty of the error amplifier circuits (Error
Amp.1, 2) according to the output voltage.
During intervals when the triangular waveform is lower than the eror amplifier output voltage, an external output
transistor is switched on.
(7) Output circuit (OUT)
The output circuit uses a totem-pole configuration and is capable of driving an external P-ch. MOS FET device.
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