Datasheet

Applications information: charging process L6924U
18/37 Doc ID 14716 Rev 2
The battery is considered deeply discharged when its voltage is lower than a threshold
(V
PRETH
), internally set to 3 V.
During the pre-charge phase, the current (I
PRECH
) 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 V
PRETH
within this
time, a fault is given (
Chapter 7.7: Maximum charging time on page 21).
If at the beginning of the charge process, the battery voltage is higher than the V
PRETH
, the
pre-charge phase is skipped.
7.2 AC or USB mode
The L6924U can charge batteries from both an AC adapter and USB inputs.
The power supply type can be chosen 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 I
AC
pin (Chapter 7.3: Fast charge phase), regardless of the resistor
connected to I
USB
.
On the other hand, 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 I
USB
pin (Chapter 7.3: Fast
charge phase
), regardless of the resistor connected to I
AC
.
Figure 10. MODE pin selection
7.3 Fast charge phase
When the battery voltage reaches the pre-charge voltage threshold (V
PRETH
), the L6924U
enters the fast-charge phase.
In this phase the device charges the battery with a constant current, whose value can be set
by external resistors connected to I
AC
pin (AC adapter mode selected) or to I
USB
pin (USB
mode) with an accuracy of 7 %.
In AC adapter mode (MODE pin low), the resistor R
AC
can be calculated as:
I
AC
R
AC
L6924U
MODE
AC adapter mode
R
USB
I
AC
R
AC
L6924U
MODE
USB mode
R
USB
I
USB
V
IN
I
USB
Sets the fast charge current
Sets the fast charge current
I
AC
R
AC
L6924U
MODE
AC adapter mode
R
USB
I
AC
R
AC
L6924U
MODE
USB mode
R
USB
I
USB
V
IN
I
USB
Sets the fast charge current
Sets the fast charge current