L6924U datasheet(20/38 Pages) STMICROELECTRONICS

20 / 38 page

Applications information: charging process

L6924U

20/38

Figure 12.

IUSB pin connection

Regardless of the operation mode (AC adapter or USB), during the fast-charge phase the

battery voltage increases until it reaches the programmed output voltage (4.2 V). A safety

timer is also present. If the Fast-charge phase does not finish within the programmed time

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

7.5

End-of-charge current

When the charge voltage approaches the battery regulated voltage (internally set to 4.2 V),

the voltage regulation phase takes place. The charge current starts to decrease until it goes

below a programmable termination current, IENDTH. This current can be selected by an

external resistor connected between the IEND pin and GND Figure 13, whose value can be

calculated as:

Equation 8

Figure 13.

IEND pin connection

Where KEND is 1050; and VMIN is 50 mV.

When the charge current goes below IENDTH, after a deglitch time, the status pins notify the

end of charge and the charge process ends.

This de-glitch time is expressed as:

Equation 9

where TMAXCH is the maximum charging time. (Chapter 7.8 on page 22)

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

ENDTH

END

MIN

END

220

MAXCH

DEGLITCH

L6924U Datasheet(PDF) 20 Page - STMicroelectronics