MB39A113 Datasheet, PDF (14/51 Pages) Fujitsu Component Limited. – ASSP for Power Supply Applications (Secondary Battery)

MB39A113
s FUNCTIONAL DESCRIPTION
1. DC/DC Converter Block
(1) Reference voltage block (REF)
The reference voltage circuit generates a temperature-compensated reference voltage (5.0 V Typ) using the
voltage supplied from the VCC terminal (pin 21) . The voltage is used as the reference voltage for the IC’s internal
circuit.
The reference voltage can be used to supply a load current of up to 1 mA to an external device through the
VREF terminal (pin 6) .
(2) Triangular wave oscillator block (OSC)
The triangular wave oscillator block has built-in a frequency setting capacitor, and generates the triangular wave
oscillation waveforms by connecting the frequency setting resistor with the RT terminal (pin 17) .
The triangular wave is input to the IC’s internal PWM comparator.
(3) Error amplifier block (Error Amp1)
The error amplifier (Error Amp1) detects voltage drop of the AC adaptor and a PWM control signal is output.
By connecting a feedback resistor and capacitor between FB12 terminal (pin 7) and −INE1 terminal (pin 8) , it
is possible to create any desired level of loop gain, thereby providing stable phase compensation to the system.
Also, it is possible to prevent rush current at power supply start-up by connecting a soft-start capacitor with the
CS terminal (pin 22) .
The use of error amplifier for soft-start detection makes it possible for a system to operate on a fixed soft-start
time that is independent of the output load.
(4) Error amplifier block (Error Amp2)
The error amplifier detects output signal of current detection amplifier (Current Amp2) and outputs PWM control
signal by comparison with +INE2 terminal (pin 3) , also controls charge current.
By connecting a feedback resistor and capacitor between FB12 terminal (pin 7) and −INE2 terminal (pin 4) , it
is possible to create any desired level of loop gain, thereby providing stable phase compensation to the system.
Also, it is possible to prevent rush current at power supply start-up by connecting a soft-start capacitor with the
CS terminal (pin 22) . The use of error amplifier for soft-start detection makes it possible for a system to operate
on a fixed soft-start time that is independent of the output load.
(5) Error amplifier block (Error Amp3)
The error amplifier (Error Amp3) detects the DC/DC converter output voltage and outputs PWM control signals.
An arbitrary output voltage can be set for 1 to 4 cells by connecting external output voltage setting resistors to
the error amplifier inverting input pins.
By connecting a feedback resistor and capacitor between FB3 terminal (pin15) and −INE3 terminal (pin 16) , it
is possible to create any desired level of loop gain, thereby providing stable phase compensation to the system.
Also, it is possible to prevent rush current at power supply start-up by connecting a soft-start capacitor with the
CS terminal (pin 22) . The use of error amplifier for soft-start detection makes it possible for a system to operate
on a fixed soft-start time that is independent of the output load.
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