MB3874 Datasheet, PDF (17/28 Pages) Fujitsu Component Limited. – DC/DC Converter IC for Parallel Charging

MB3874/MB3876
s METHOD OF SETTING THE CHARGING CURRENT
The charge current (output control current) value can be set with the voltage at the +INE2, +INE3 terminal.
If a current exceeding the set value attempts to flow, the charge voltage drops according to the set current value.
Battery 1 charge current setting voltage : +INE2
+INE2 (V) = 25 × I1 (A) × RS1 (Ω)
Battery 2 charge current setting voltage : +INE3
+INE3 (V) = 25 × I2 (A) × RS 2 (Ω)
s METHOD OF SETTING THE SOFT START TIME
Upon activation, the IC starts charging the capacitor (Cs) connected to the CS terminal .
The error amplifier causes soft start operation to be performed with the output voltage in proportion to the CS
pin 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 SETTING
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) =: 14444 / RT (kΩ)
s AC ADAPTER VOLTAGE DETECTION
When partial potential point A of the AC adapter voltage (Vcc) becomes lower than the voltage at the –INE1
pin, the IC enters the constant-power mode to reduce the charge current in order to keep AC adapter power
constant.
AC adapter detected voltage setting Vth
Vth (V) = (208k + 42k) / 42k × − INE1 =: 5.95 × − INE1
− INE1 setting voltage range : 1.176 V to 4.2 V (equivalent to 7 V to 25 V for Vcc)
−INE1
8
<Error Amp.1>
−
A
VCC
+
208 kΩ
42 kΩ
17