MB39A114 Datasheet, PDF (16/54 Pages) Fuji Electric – DC/DC Converter IC for Charging Li-ion Battery

MB39A114
s FUNCTIONAL DESCRIPTION
1. DC/DC Converter Block
(1) Reference voltage block (REF)
The reference voltage circuit generator uses the voltage supplied from the VCC terminal (pin 21) to generate a
temperature compensated stable voltage (5.0 V Typ) used as the reference supply voltage for the internal circuits
of the IC. It is also possible to supply the load current of up to 1 mA to external circuits as a output reference
voltage through the VREF terminal (pin 6) .
(2) Triangular wave oscillator block (OSC)
The triangular wave oscillator block has built-in capacitor for frequency setting, and generates the triangular
wave oscillation waveform by connecting the freguency setting resistor with the RT terminal (pin 17) .
The triangular wave is input to the PWM comparator circuits on the IC.
(3) Error amplifier block (Error Amp1)
The error amplifier (Error Amp1) detects voltage drop of the AC adapter and outputs a PWM control signal.
Also, by connecting feedback resistor and capacitor between FB12 terminal (pin 7) and −INE1 terminal (pin 8),
it is possible to set the desired level of loop gain, to provide stabilized phase compensation to the system.
The CS terminal (pin 22) can be connected to a soft-start capacitor to prevent rush currents at startup. The soft
start time is detected by the error amplifier, which provides a constant soft-start time independent of output load.
(4) Error amplifier block (Error Amp2)
The amplifier detects output signal from the current detection amplifier (Current Amp 2) . This is amplifier providing
PWM control signal by comparing to +INE2 terminal (pin3), and it is used to control the charging current.
Also, by connecting feedback resistor and capacitor between FB12 terminal (pin 7) and −INE2 terminal
(pin 4) , it is possible to set the desired level of loop gain, to provide stabilized phase compensation to the system.
The CS terminal (pin 22) can be connected to a soft-start capacitor to prevent rush currents at startup. The soft
start time is detected by the error amplifier, which provides a constant soft-start time independent of output load.
(5) Error amplifier block (Error Amp3)
The error amplifier (Error Amp3) detects output voltage of the DC/DC converter and outputs a PWM control
signal. Output voltage become 16.8 V if the SEL terminal is set in “H” level, and become 12.6 V if it sets in “L” level .
Also, by connecting feedback resistor and capacitor between FB3 terminal (pin 15) and −INE3 terminal
(pin 16) , it is possible to set the desired level of loop gain, to provide stabilized phase compensation to the system.
The CS terminal (pin 22) can be connected to a soft-start capacitor to prevent rush currents at startup. The soft
start time is detected by the error amplifier, which provides a constant soft-start time independent of output load.
(6) Current detection amplifier block (Current Amp1)
The current detection amplifier (Current Amp1) detects a voltage drop which occurs between both ends of the
output sense resistor (RS) due to the flow of the charge current, using the +INC1 terminal (pin 13) and −INC1
terminal (pin 12) . Then it outputs the signal amplified by 20 times to the error amplifier (Error amp1) at the next
stage.
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