MB39A125 Datasheet, PDF (24/64 Pages) Fujitsu Component Limited. – DC/DC Converter IC for Charging Li-ion Battery

MB39A125/126
■ FUNCTIONAL DESCRIPTION
1. DC/DC Converter Block
(1) Reference voltage block (REF)
The reference voltage circuit 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 power supply voltage for the IC’s internal circuitry.
This block can also be used to obtain a load current to a maximum of 1 mA from the reference voltage VREF
terminal (pin 6) .
(2) Triangular wave oscillator block (OSC)
The triangular wave oscillator block has built-in capacitor for frequency setting into and generates the triangular
wave oscillation waveform by connecting the frequency 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)
This amplifier detects the output signal from the current detection amplifier (Current Amp1) , compares this to
the +INE1 terminal (pin 9) , and outputs a PWM control signal to be used in controlling the charge current.
In addition, an arbitrary loop gain can be set up by connecting a feedback resistor and capacitor between the
FB123 terminal (pin 15) and −INE1 terminal (pin 8) , providing stable phase compensation to the system.
(4) Error amplifier block (Error Amp2)
This amplifier detects the output signal from the current detection amplifier (Current Amp2) , compares this to
the +INE2 terminal (pin 3) , and outputs a PWM control signal to be used in controlling the charge current.
In addition, an arbitrary loop gain can be set up by connecting a feedback resistor and capacitor between the
FB123 terminal (pin 15) and −INE2 terminal (pin 4) , providing stable phase compensation to the system.
(5) Error amplifier block (Error Amp3)
This error amplifier (Error Amp3) detects the output voltage from the DC/DC converter and outputs the PWM
control signal. MB39A125 can set the desired level of output voltage from 1 cell to 4 cells by connecting external
output voltage setting resistors to the error amplifier inverted input terminal. MB39A126 can set the output voltage
for 3 cells or 4 cells by SEL terminal (pin 11) input.
In addition, an arbitrary loop gain can be set by connecting a feedback resistor and capacitor from the FB123
terminal (pin 15) to the −INE3 terminal (pin 16) , enabling stable phase compensation to the system.
(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 (RS2) due to the flow of the charge current, using the +INC1 terminal (pin 13) and −INC1
terminal (pin 12) . The signal amplified to 20 times is output to the OUTC1 terminal (pin 10) .
24