MB3879 データシートの表示（PDF） - Fujitsu

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MB3879

DC/DC Converter IC for Parallel Charging of 3/4 cell Li-ion & NiMH Batteries

Fujitsu 

MB3879

s FUNCTIONS

1. DC/DC Converter Functions

(1) Reference voltage block (REF)

The reference voltage generator (REF) generates a temperature-compensated reference voltage from the volt-

age supplied from the VCC terminal (pin 1). The voltage is used as the reference voltage for Error Amp.

(2) Control bias voltage block (VB)

The control bias voltage block (VB) generates a temperature-compensated reference voltage using internal

reference voltage (5.0V Typ) from VB terminal. The voltage is used as the reference voltage for the IC’s internal

circuitry.

The reference voltage can be used to supply a load current of up to 1 mA to an external device through the VB

terminal

(3) Triangular waveform oscillator block (OSC)

The triangular wave oscillation frequency setting resistor is built in, and the triangular wave oscillation waveform

(amplitude of 1.6 V to 2.6 V) is generated by connecting the triangular wave oscillation frequency setting capacitor

with the CT terminal (pin 37) .

The triangular oscillation waveform is input to the PWM comparator on the IC.

(4) Error amplifier block (Error Amp1)

The error amplifier (Error Amp1) controls the charge current with the amplifier which outputs the PWM control

signal detecting the total current of the system current and control IC input current. It supports a wide range of

common mode input voltages from "0 V to Vcc - 1.8 V".

In addition, an arbitrary loop gain can be set by connecting a feedback resistor and capacitor from FB1 terminal

to -INE1 terminal, enabling stable phase compensation to be provided for the system.

This section also outputs signal to mode detection section.

(5) Error amplifier block (Error Amp2)

The error amplifier (Error Amp2) detects the dropping voltage of AC adapter by connecting an external resistor

to +INE2 terminal (pin 40), and outputs PWM control signals. It supports a wide range of common mode input

voltages from "0 V to Vcc - 1.8 V".

In addition, an arbitrary loop gain can be set by connecting a feedback resistor and capacitor from FB2 terminal

(pin 42) to −INE2 terminal (pin 41), enabling stable phase compensation to be provided for the system.

This block also outputs signal to mode detection block.

(6) Error amplifiers block (Error Amp3 and Error Amp4)

The error amplifiers (Error Amp3 and Error Amp4) detect the output voltages of current detection amplifiers

(Current Amp2 and Current Amp3) and compare the voltages with ones on +INE3 terminal (pin 19) and +INE4

terminal (pin 31), and then outputting PWM control signal. This block controls charge currents.

In addition, an arbitrary loop gain can be set by connecting a feedback resistor from FB3 terminal (pin 16) to -

INE3 terminal (pin 18) and from FB4 terminal (pin 34) to -INE4 terminal (pin 32) and capacitor, enabling stable

phase compensation to be provided for the system.

This block also outputs signal to mode detection block.

By connecting a soft-start capacitor to CS1 terminal (pin 23), an inrush current upon power supply startup is

prevented. By detecting soft-start with the error amplifier, soft-start time becomes constant, being independent

of output loads.

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