L6924UTR datasheet(12/37 Pages) STMICROELECTRONICS

12 / 37 page

Operation description

L6924U

12/37

Doc ID 14716 Rev 2

Figure 5.

Li-Ion charging profile

6.1

Linear mode

When operating in linear mode, the device works in a way similar to a linear regulator with a

constant current limit protection.

It charges the battery in three phases:

●

Pre-charging current ("pre-charge" phase).

●

Constant current ("fast-charge" phase).

●

Constant voltage ("voltage regulation" phase).

VADP is the output voltage of the upstream AC-DC adapter that is, in turn, the input voltage

of the L6924U. If the battery voltage is lower than the default pre-charge voltage (VPRETH),

the pre-charge phase takes place. The battery is pre-charged with a low current, internally

set to 10 % of the fast charge current.

When the battery voltage goes higher than VPRETH, the battery is charged with the fast

charge current (IUSB or IAC according to the selection of the MODE pin).

Finally, when the battery voltage is close to the regulated output voltage (4.2 V), the voltage

regulation phase takes place and the charging current is reduced. The charging process

ends when the charging current reaches the programmed value (IENDTH) or when the

charging timer expires.

Figure 6 shows the different phases.

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

0.500

200

400

600

800

1000

1200

Charging time (sec)

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

4.000

4.500

Ichg

Vbatt

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