L6924U datasheet(18/38 Pages) STMICROELECTRONICS

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Applications information: charging process

L6924U

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7.2

Pre-charge phase

The L6924U allows pre-charging the battery with a low current when the battery is deeply

discharged.

The battery is considered deeply discharged when its voltage is lower than a threshold

(VPRETH), internally set to 3 V.

During pre-charge phase, the current (IPRECH) has a default value equal to 10 % of the fast-

charge current.

A safety timer is also present. If the battery voltage does not rise over VPRETH within this

time, a fault is given (Chapter 7.8: Maximum charging time on page 22).

If at the beginning of the charge process, the battery voltage is higher than the VPRETH, the

pre-charge phase is skipped.

7.3

AC or USB mode

The L6924U can charge batteries from both AC adapter and USB inputs.

The choice of the power supply is done by driving the MODE pin.

A low level sets the L6924U in AC mode. The fast charge current is determined by the

resistor connected to the IAC pin (Chapter 7.4: Fast charge phase), regardless the resistor

connected to IUSB.

The same way, a high level at the MODE pin sets the L6924U in USB mode. The fast charge

current is determined by the resistor connected to the IUSB pin (Chapter 7.4: Fast charge

phase), regardless the resistor connected to IAC.

Figure 10.

MODE pin selection

L6924U

MODE

AC adapter mode

USB

L6924U

MODE

USB mode

USB

Sets the fast charge current

L6924U

MODE

AC adapter mode

USB

L6924U

MODE

USB mode

USB

Sets the fast charge current

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