MB3874 Fujitsu Media Devices, MB3874 Datasheet - Page 18

• Manufacturer Part Number: MB3874
• Description: DC/DC Converter IC for Parallel Charging
• Manufacturer: Fujitsu Media Devices

18
MB3874/MB3876
Err Amp.2 3
Err Amp.4 5
Err Amp.1
OPERATION TIMING DIAGRAM
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
OUT
OUTM
controlled charging
AC adapter dynamically-
FB2,3
FB4
FB1
V
AC
Adaptor
IN
Constant voltage
control
Mode
Signal
Battery
Charger
MB3874
MB3876
Constant current control
Ichg
Battery
ISYS
AC adapter dynamically-
controlled charging
System
Power
2.8 V
2.5 V
1.5 V