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FUNCTIONAL DESCRIPTION
1. DC/DC Converter Unit
(1) Reference voltage block (REF)
The reference voltage generator uses the voltage supplied from the VCC terminal (pin 1) to generate a
temperature compensated, stable voltage (5.0V Typ) used as the reference supply voltage for the IC’s internal
circuitry.
This terminal can also be used to obtain a load current to a maximum of 1 mA from the reference voltage VREF
terminal (pin 21) .
(2) Triangular wave oscillator block (OSC)
The triangular wave oscillator builds the capacitor for frequency setting into, and generates the triangular wave
oscillation waveform by connecting the frequency setting resistor with the RT termi nal (pin 20) .
The triangular wave is input to the PWM comparator on the IC.
(3) Error amplifier block (Error Amp1)
This amplifier detects the output signal from the current detection amplifier (Current Amp2) , compares this to
the +INE1 terminal (pin 7) , and outputs a PWM control signal to be used in controlling the charging current.
A double constant current value can be set together with the charging current control with error amplifier (Error
Amp.2). Therefore, the fail safe control with high safety or more can be achieved.
In addition, an arbitrary loop gain can be set up by connecting a feedback resistor and capacitor between the
FB1 terminal (pin 9) and -INE1 terminal (pin 8) , providing stable phase compensation to the system.
Connecting a soft-start capacitor to the CS terminal (pin 19) prevents rush currents when the IC is turned on.
Using an error amplifier for soft-start detection makes the soft-start time constant, independent of the output
load.
It is possible to correspond also to dynamic control charge (Dynamically-controlled charging) by which the
constant current control and the voltage drop of AC adaptor is detected by combining with current detection
amplifier (Current Amp1).
(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 13) , and outputs a PWM control signal to be used in controlling the charging current.
In addition, an arbitrary loop gain can be set up by connecting a feedback resistor and capacitor between the
FB2 terminal (pin 15) and –INE2 terminal (pin 14) , providing stable phase compensation to the system.
Connecting a soft-start capacitor to the CS terminal (pin 19) prevents rush currents when the IC is turned on.
Using an error amplifier for soft-start detection makes the soft-start time constant, independent of the output
load.
(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. External output voltage setting resistors can be connected to the error amplifier inverted input
terminal to set the desired level of output voltage from 1 cell to 4 cells.
In addition, an arbitrary loop gain can be set by connecting a feedback resistor and capacitor from the FB3
terminal (pin 17) to the -INE3 terminal (pin 16) of the error amplifier, enabling stable phase compensation to
the system.
Connecting a soft-start capacitor to the CS terminal (pin 19) prevents rush currents when the IC is turned on.
Using an error amplifier for soft-start detection makes the soft-start time constant, independent of the 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 (R
S2
) due to the flow of the AC adapter current, using the +INC1 terminal (pin 5) and
-INC1 terminal (pin 4) . Then it outputs the signal amplified by 25 times to the OUTC1 terminal (pin 3).
Moreover, an equal offset voltage to the voltage impressed to the IOFA1 terminal (pin 6) can be set.
(7) Current detection amplifier block (Current Amp2)
The current detection amplifier (Current Amp2) detects a voltage drop which occurs between both ends of the
output sense resistor (R
S1
) due to the flow of the AC adapter current, using the +INC2 terminal (pin 12) and
–INC2 terminal (pin 11) . Then it outputs the signal amplified by 25 times to the OUTC2 terminal (pin 10).