MIC79050 datasheet(12/28 Pages) MICROCHIP

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MIC79050

DS20005771B-page 12



2017 - 2022 Microchip Technology Inc. and its subsidiaries.

FIGURE 5-3:

Charging Cycles.

FIGURE 5-4:

Protected Constant-Current Charger.

5.3

Protected Constant-Current

Charger

Another form of charging is using a simple wall adapter

that offers a fixed voltage at a controlled, maximum

current rating. The output of a typical charger will

source a fixed voltage at a maximum current unless

that maximum current is exceeded. In the event that

the maximum current is exceeded, the voltage will drop

while maintaining that maximum current. Using an

MIC79050 after this type of charger is ideal for

lithium-ion battery charging. The only obstacle is end of

charger termination. Using a simple differential

amplifier and a similar comparator and reference

circuit, similar to Figure 5-1, completes a single cell

lithium-ion battery charger solution.

Figure 5-4 shows this solution in completion. The

source is a fixed 5V source capable of a maximum of

400 mA of current. When the battery demands full

current (fast charge), the source will provide only

400 mA and the input will be pulled down. The output

of the MIC79050 will follow the input minus a small

voltage drop. When the battery approaches full charge,

the current will taper off. As the current across RS

approaches 50 mA, the output of the differential

amplifier (MIC7300) will approach 1.225V, the

reference voltage set by the LM4041. When it drops

below the reference voltage, the output of the

comparator (MIC6270) will allow the base of Q1 to be

pulled high through R2.

VEOC

Open Circuit

Charger Voltage

Battery Current (IB)

Battery Voltage (VB)

Unregulated Input

Voltage(VB)

79050 Programmed

Output Voltage

(No LoadVoltage)

End of Charge (VEOC)

State A

Initial Charge

State B

Voltage Charge

State C

End of Charge

State D

Charge Top

State C

BAT

GND

MIC79050-4.2YM

LM4041

CIM3-1.2

5V 5%@

400mA 5%

4.7μF

8.06M

47k

10k

MIC6270

MIC7300

10k

Li-Ion

Cell

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