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MB3832A

DC/DC Converter IC for Charging

Fujitsu 

MB3832A

s FUNCTIONAL DESCRIPTION

1. Switching Regulator Functions

(1) Reference voltage circuit (Ref)

The reference voltage generator uses the voltage supplied from the VCC terminal (pin 18) to generate a temper-

ature-compensated, stable voltage (about 2.50 V) as the reference supply voltage for the IC’s internal circuitry.

The reference voltage can be output, up to 1 mA, to an external device through the VREF terminal (pin 1).

(2) Triangular wave oscillator (OSC)

The triangular wave oscillator generates a triangular waveform with a timing capacitor and a timing resistor

respectively connected to the CT terminal (pin 3) and RT terminal (pin 2).

The triangular wave is input to the PWM comparator in the IC while it can also be supplied to an external device

through the CT terminal. In addition, the oscillator can be used for external synchronization, where it generates

a triangular wave synchronous to the input signal from the SYNC terminal (pin 4).

(3) Error amplifiers (Error Amp. 1, 2)

The error amplifiers detect the output voltage from the switching regulator and outputs the PWM control signal.

It supports a wide range of in-phase inputs from 0 V to “VCC – 0.9 V”. An arbitrary loop gain can be set by

connecting a feedback resistor and capacitor from the FB1 terminal (pin 6) [FB2 terminal (pin 15)] to the –IN1

terminal (pin 7) [–IN2 terminal (pin 14)] of the error amplifier, enabling stable phase compensation to the system.

(4) Current detector amplifier (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. At the same

time, the amplifier converts the voltage to the GND-reference voltage level and outputs it to the COUT terminal

(pin 12). It can also control the charging current in combination with the error amplifier circuit.

(5) Power control circuit (CTL)

The power control circuit can control turning on and off the power supply through the CTL terminal (pin 17).

(Supply current in standby mode: About 0 µA)

Depending on the voltage level of the PWM Comp. input terminal, the OUT terminal (pin 19) may become “L”

level during discharging of the VREF voltage after the CTL terminal is turned off with a capacitor connected to the

VREF terminal. The power control circuit contains a function for fixing the OUT output terminal to the “H” level

when CTL = “L” and VREF = “H”, preventing inadvertent “L” level output after turning the CTL terminal off.

(6) PWM comparator circuit (PWM Comp.)

The PWM comparator circuit is a voltage-pulse width converter for controlling the output duty of the error

amplifiers (Error Amp. 1, 2) depending on their output voltage.

The PWM comparator circuit turns on the external output transistor during the interval in which the triangular

wave voltage level is lower than the voltage level at both of the error amplifier output terminals (FB1 terminal

(pin 6), FB2 terminal (pin 15)) and the DTC terminal (pin 16).

(7) Output circuit (Out)

The output circuit uses a totem-pole configuration, capable of driving an external P-channel MOS FET and PNP

transistor. It can also control the output sink current with a resistor connected between the VE terminal

(pin 20) and the GND terminal (pin 11).

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