Datasheet

Applications information: charging process L6924D
18/38 Doc ID 11908 Rev 9
Equation 8
Figure 12. V
PRE
pin connection
Where R
VPRE
is the resistor between V
PRE
and GND, and R
PRG
is the resistor used to set
the charge current (see Section 7.4: Fast charge current), and V
PRETH
is the selected
threshold.
A safety timer is also present. If the battery voltage doesn't rise over V
PRETH
, before this
time is expired, a fault is given (see Section 7.8: Maximum charging time). If at the beginning
of the charge process, the battery voltage is higher than the V
PRETH
, the Pre-Charge phase
is skipped.
7.4 Fast charge current
When the battery voltage reaches the Pre-charge voltage threshold (V
PRETH
), the L6924D
starts the Fast-charge Phase. In this phase, the device charges the battery with a constant
current, I
CHG
, programmable by an external resistor that sets the charge current with an
accuracy of 7% Figure 13. The equation used to select the R
PRG
as follows:
Equation 9
Figure 13. I
PRG
pin connection
Where K
PRG
is a constant, equal to 9500.
During this phase, the battery voltage increases until it reaches the programmed output
voltage. A safety timer is also present. If this time expires, a fault is given (Section 7.8:
Maximum charging time).
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×=
ltPRETHDefau
PRETH
PRGVPRE
V
V
RR
V
PRE
L6924D
R
PRE
V
PRE
L6924D
R
PRE
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×=
CHG
PRG
BGPRG
I
K
VR