FUJITSU MB3878 - Manual (Page 15)

MB3878
15
■ ■ ■ ■ AC ADAPTOR VOLTAGE DETECTION
With an external resistor connected to the +INE2 terminal(pin 3), the IC enters the dynamically-controlled
charging mode to reduce the charge current to keep AC adaptor power constant when the partial potential point
A of the AC adaptor voltage (Vcc) becomes lower than the voltage at the -INE2 terminal.
AC adaptor detected voltage setting: Vth
Vth (V)
=
(R1
+
R2)
/
R2
× −
INE2
−
INE2 setting voltage range : 1.176 V to 4.2 V (equivalent to 7 V to 25 V for Vcc)
■ ■ ■ ■ OPERATION TIMING DIAGRAM
−
+
V CC
R1
R2
+ INE2
−
INE2
A
<Error Amp.2>
4
3
2.5 V
1.5 V
Error Amp.1
Error Amp.3
Error Amp.2
FB1
FB3
FB2
OUT
Constant
voltage control AC adaptor dynamically-
controlled charging Constant current control AC adaptor dynamically-
controlled charging