Datasheet

L6924U Applications information: charging process
Doc ID 14716 Rev 2 19/37
Equation 6
Where V
BG
is the internal reference equal to 1.23 V, whereas K
PRG
is a constant equal to
9500.
Figure 11. I
AC
pin connection
In USB mode (MODE pin high), the R
USB
resistor can be selected as:
Equation 7
Where V
BG
and K
PRG
have the same meaning and value above mentioned.
The charge current in USB mode depends on R
USB
as well as the state of the ISEL pin.
When this pin is high, the “high-power” USB mode is selected and the charge current is
determined by the equation 7.
The charge current in USB mode should be set in accordance with the typical USB current
capability (up to 500 mA). If ISEL is low, the “low-power” USB mode is selected and the
charge current is a fifth of the high-power USB mode charge current (up to 100 mA)
During low power USB mode operation, since the charge current is reduced by one fifth, the
maximum charging time is proportionally increased (
Section 7.7: Maximum charging time).
Figure 12. I
USB
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 7.7: Maximum charging time on page 21), a fault is given.
PRG
AC
BG
AC
K
I
V
R ⋅
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
PRG
USB
BG
USB
K
I
V
R ⋅
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=