MIC79050_05 MICREL [Micrel Semiconductor], MIC79050_05 Datasheet - Page 8

• Manufacturer Part Number: MIC79050_05
• Description: Simple Lithium-Ion Battery Charger
• Manufacturer: MICREL [Micrel Semiconductor]

MIC79050
The Charging Cycle (See Figure 1C.)
1. State A: Initial charge. Here the battery’s charging cur-
2. State B: Constant voltage charge. Here the battery
MIC79050
rent is limited by the wall adapter’s natural impedance.
The battery voltage approaches 4.2V.
voltage is at 4.2V ± 0.75% and the current is decaying
in the battery. When the battery has reached approxi-
mately 1/10th of its 1C rating, the battery is considered
to have reached full charge. Because of the natural
characteristic impedance of the cheap wall adapters, as
the battery voltage decreases so the input voltage in-
creases. The MIC6270 and the LM4041 are configured
as a simple voltage monitor, indicating when the input
400mA 5%
End of Charge (V
5V 5%@
79050 Programmed
Battery Voltage (V
Battery Current (I
Unregulated Input
Output Voltage
(No LoadVoltage)
Voltage(V
0.050Ω
EOC
Figure 2. Protected Constant-Current Charger
B
B
B
)
)
)
)
Initial Charge
1k
1k
State A
Figure 1C. Charging Cycles
47k
MIC7300
Voltage Charge
State B
V
EOC
47k
MIC79050-4.2BM
8
Charger Voltage
IN
EN
Open Circuit
3. State C: End of charge cycle. When the input voltage,
4. State D: Top up charge. As soon as enough current
Variations on this scheme can be implemented, such as the
circuit shown in Figure 2.
For those designs that have a zero impedance source , see
Figure 3.
GND
End of Charge
State C
voltage has reached such a level so the current in the
battery is low, indicating full charge.
V
is drawn out of the input source, which pulls the volt-
age lower than the V
pulled low and charging will initiate.
BAT
S
FB
reaches V
CIM3-1.2
LM4041
Q1
8.06M
Charge Top
State D
10k
EOC,
4.7µF
MIC6270
an end of charge signal is indicated.
EOC
State C
, the end of charge flag will be
10k
R2
August 2005
Micrel, Inc.