MB3878 Datasheet, PDF (14/24 Pages) Fujitsu Component Limited. – DC/DC Converter IC for Charging

MB3878
s SETTING THE CHARGING VOLTAGE
The charging voltage (DC/DC output voltage) can be set by connecting external voltage setting resistors (R3,
R4) to the -INE3 terminal. Be sure to select a resistor value that allows you to ignore the on resistor (70 Ω, 1mA)
of the internal FET connected to the OUTD terminal (pin 11).
Battery charging voltage: VO
VO (V) = (R3 + R4) / R4 × 4.2 (V)
B ^VO
R3
−INE3
16
R4
11
OUTD
< Error Amp.3 >
−
+
+
4.2 V
22
CS
s METHOD OF SETTING THE CHARGING CURRENT
The charge current (output control current) value can be set with the voltage at the +INE1 terminal (pin 9).
If a current exceeding the set value attempts to flow, the charge voltage drops according to the set current value.
Battery charge current setting voltage : +INE1
+INE1 (V) = 25 × I1 (A) × RS (Ω)
s METHOD OF SETTING THE SOFT START TIME
Upon activation, the IC starts charging the capacitor (Cs) connected to the CS terminal (pin 22).
The error amplifier causes soft start operation to be performed with the output voltage in proportion to the CS
terminal voltage regardless of the load current of the DC/DC converter.
Soft start time: ts (Time taken for the output voltage to reach 100 %)
ts (s) =: 4.2 × CS (µF)
s METHOD OF SETTING THE TRIANGULAR WAVE OSCILLATOR FREQUENCY
The trianguar wave oscillator frequency can be set by the timing resistor (RT) connected the RT terminal (pin 17).
Triangular wave oscillator frequency: fOSC
fOSC (kHz) =: 13630 / RT (kΩ)
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