Datasheet

V
RECH
(V
WAKE
)
V
LOWV
(V
DISCH
)
Battery
inserted
Batterynotdetected
t
WAKE
Batterydetected
t
LOWV_DEG
t
RECH_DEG
V
REG
DISCH DISCH
MAX
2
1
I t
C =
R
0.5 1+
R
´
é ù
´
ê ú
ë û
MAX
6 mA 1 sec
C = = 2000 μF
500 k
0.5 1+
100 k
´
W
é ù
´
ê ú
W
ë û
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www.ti.com SLUSA75 –JULY 2010
Figure 20. Battery Detect Timing Diagram
Care must be taken that the total output capacitance at the battery node is not so large that the discharge current
source cannot pull the V
FB
voltage below the LOWV threshold during the 1 second discharge time. The
maximum output capacitance can be calculated according to Equation 9:
(9)
Where C
MAX
is the maximum output capacitance, I
DISCH
is the discharge current, t
DISCH
is the discharge time, and
R
2
and R
1
are the voltage feedback resistors from the battery to the VFB pin. The 0.5 factor is the difference
between the RECHARGE and the LOWV thresholds at the VFB pin.
Example
For a 3-cell Li+ charger, with R
2
= 500kΩ, R
1
= 100kΩ (giving 12.6V for voltage regulation), I
DISCH
= 6mA, t
DISCH
= 1 second.
(10)
Based on these calculations, no more than 2000 µF should be allowed on the battery node for proper operation
of the battery detection circuit.
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