Fujitsu MB3887 Datasheet page 18

MB3887
3. Soft-Start Function
Soft-start block (SOFT)
Connecting a capacitor to the CS terminal (pin 22) prevents rush currents when the IC is turned on. Using an
error amplifier for soft-start detection makes the soft-start time constant, being independent of the output load
of the DC/DC converter.
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 (pin 16) . Be sure to select a resistor value that allows you to ignore the on-resistor
(35 , 1mA) of the internal FET connected to the OUTD terminal (pin 11) . In standby mode, the charging
voltage is applied to OUTD termial. Therefore, output voltage must be adjusted so that voltage applied to OUTD
terminal is 17 V or less.
Battery charging voltage : V
V (V) (R3 R4)
O
METHOD OF SETTING THE CHARGING CURRENT
The charge current (output limit 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) 20
METHOD OF SETTING THE TRIANGULAR WAVE OSCILLATION FREQUENCY
The triangular wave oscillation frequency can be set by the timing resistor (R
Triangular wave oscillation frequency : f
f (kHz) : = 13630 R
OSC
18
O
R4 4.2 (V)
V
O
B
R3
INE3
16
R4
11
OUTD
22
CS
I1 (A) R ( )
S
OSC
(k )
T
<Error Amp3>
4.2 V
) connected the RT terminal (pin 17) .
T