L6924D datasheet(14/38 Pages) STMICROELECTRONICS

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Operation description

L6924D

14/38

The worst case in power dissipation occurs when the device starts the Fast-Charge Phase. In

fact, the battery voltage is at its minimum value. In this case, this is the maximum difference

between the adapter voltage and battery voltage, and the charge current is at its maximum

value.

The power dissipated is given by the following formula:

The higher the adapter voltage is, the higher the power dissipated. The maximum power

dissipated depends on the thermal impedance of the device mounted on board.

6.2

Quasi-pulse mode

The Quasi-Pulse Mode can be used when the system can rely on the current limit of the

upstream adapter to charge the battery. In this case, ICHG must be set higher than the current

limit of the adapter. In this mode, the L6924D charges the battery with the same three phases

as in Linear Mode, but the power dissipation is greatly reduced as shown in Figure 7.

Figure 7.

Typical charge curves in quasi pulse mode

CHG

BAT

ADP

DIS

−

)

(

Eq. 7-1

Adapter Voltage

Charge Current

Power dissipation

Battery Voltage

End

Charge

Voltage Regulation

Phase

Pre-Charge

Phase

Fast-Charge

Phase

LIM

Ilim x Rdson

PRETH

CHG

PRETH

OPRGTH

ADP

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