Datasheet

V
RECH
V
LOWV
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
1.425 1+
R
´
é ù
´
ê ú
ë û
MAX
8mA 1sec
C = = 930 F
500k
1.425 1+
100k
´
m
é ù
´
ê ú
ë û
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SLUS893A –MARCH 2010– REVISED OCTOBER 2011 www.ti.com
Figure 16. 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 voltage below the LOWV threshold during the 1-second discharge time. The maximum
output capacitance can be calculated as seen in Equation 8:
(8)
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 1.425 factor is the difference
between the RECHARGE and the LOWV thresholds at the VFB pin.
EXAMPLE
For a 3-cell Li+ charger, with R2 = 500 kΩ, R1 = 100 kΩ (giving 10.8 V for voltage regulation), I
DISCH
= 8 mA,
t
DISCH
= 1 second,
(9)
Based on these calculations, no more than 930 μF should be allowed on the battery node for proper operation of
the battery detection circuit.
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