MB3874 Datasheet, PDF (18/28 Pages) Fujitsu Component Limited. – DC/DC Converter IC for Parallel Charging

MB3874/MB3876
s OPERATION TIMING DIAGRAM
Err Amp.2, 3 FB2,3
Err Amp.4, 5 FB4
Err Amp.1 FB1
OUT
AC adapter dynamically- Constant voltage
controlled charging
control
OUTM
Constant current control
2.8 V
2.5 V
1.5 V
AC adapter dynamically-
controlled charging
About the OUTM signal
The OUTM signal becomes low when the output voltage of the error amplifier (Error Amp. 1) that detects the
AC adapter voltage (Vcc) becomes lower than the crest value (2.5 V) of the triangular waveform generator (OSC).
If the sum of the current consumption by the system and that by the charger exceeds the current capacity of the
AC adapter, the IC detects a voltage drop in the AC adapter output and switches to the dynamically-controlled
charging mode from C.V.C.C (constant-voltage/constant-current charging control) mode.
In the dynamically-controlled charging mode, the OUTM pin outputs the L level signal to distinguish between
the case in which the charge current has become small as the system current consumption has increased and
the case in which it has become small as battery charging has been finished.
L: Dynamically-controlled charging
H: C.V.C.C (constant-voltage/constant-current charging control) or IC standby mode
VIN
AC
Adaptor
Mode
Signal
Battery
Charger
MB3874
MB3876
ISYS
System
Power
Ichg
Battery
18