Datasheet

L6924D Applications information: charging process
Doc ID 11908 Rev 9 17/38
7.2 Pre-charge current
The L6924D allows pre-charging the battery with a low current when the battery voltage is
lower than a specified threshold (V
PRETH
). The Pre-charge current has a default value equal
to 10% of the fast-charge current. However it can be adjusted by connecting a resistor from
the I
PRE
pin to GND or V
REF
(see Figure 10). When the resistor is connected between I
PRE
pin and GND, the current is higher than the default value. The R
PRE
value is given by:
Equation 6
Figure 10. I
PRE
pin connection
When R
PRE
is connected to V
REF
, the current is lower than the default value. V
REF
is the
external reference equal to 1.8 V, V
BG
is the internal reference equal to 1.23 V and K
PRE
is a
constant equal to 950. See Figure 11.
The relationship is shown in the equation 7:
Equation 7
Figure 11. I
PRE
pin connection
7.3 Pre-charge voltage
If the V
PRE
pin is floating, a default value of V
PRETH
is set, equal to 2.8 V (V
PRETHDefault
).
Otherwise, the device offers the possibility to program this value, with a resistor connected
between the V
PRE
pin and GND (see Figure 12). In this case, the R
VPRE
is given by the
equation 8:
PRG
BG
PRE
PRECH
BG
PRE
R
V
K
I
V
R
−
=
L6924D
I
PRE
L6924D
I
PRE
PRE
PRECH
PRG
BG
BG
REF
PRE
K
I
R
V
VV
R
−
−
=
V
REF
L6924D
I
PRE
V
REF
L6924D
I
PRE