FUJITSU MB3878 - Manual (Page 14)

MB3878
14
■ ■ ■ ■ 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: V
O
V
O
(V)
=
(R3
+
R4)
/
R4
×
4.2 (V)
■ ■ ■ ■ 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)
×
R
S
(
Ω
)
■ ■ ■ ■ 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
×
C
S
(
µ
F)
■ ■ ■ ■ METHOD OF SETTING THE TRIANGULAR WAVE OSCILLATOR FREQUENCY
The trianguar wave oscillator frequency can be set by the timing resistor (R
T
) connected the RT terminal (pin 17).
Triangular wave oscillator frequency: f
OSC
f
OSC
(kHz) := 13630 / R
T
(k
Ω
)
< Error Amp.3 >
−
+
+
4.2 V
R3
V O
R4
−
INE3
OUTD
CS
16
B
11
22