L6924D datasheet(13/38 Pages) STMICROELECTRONICS

13 / 38 page

L6924D

Operation description

13/38

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 L6924D. If the battery voltage is lower than a set pre-charge voltage (VPRETH), the pre-

charge phase takes place. The battery is pre-charged with a low current IPRE (Chapter 7.2 on

page 18).

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

current ICHG, set with an external resistor (Chapter 7.4 on page 19).

Finally, when the battery voltage is close to the regulated output voltage VOPRGTH (4.1V or

4.2V), the voltage regulation phase takes place and the charging current is reduced. The

charging process usually is terminated when the charging current reaches a set value or when

a charging timer expires (Chapter 7.9 on page 23).

Figure 6 shows the different phases.

Figure 6.

Typical charge curves in linear mode

End

Charge

Voltage-Regulation

Phase

Power dissipation

Pre-Charge

Phase

Fast-Charge

Phase

PRETH

CHG

OPRGTH

Battery Voltage

Charge Current

Adapter Voltage

ADP

PRETH

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