Datasheet

MAX
8mA 1sec
C = = 2.7 mF
500k
0.5 1+
100k
´
é ù
´
ê ú
ë û
DISCH DISCH
MAX
2
1
I t
C =
R
0.5 1+
R
´
é ù
´
ê ú
ë û
V
RECH
V
LOWV
Battery
inserted
Batterynotdetected
t
WAKE
Batterydetected
t
LOWV_DEG
t
RECH_DEG
V
REG
( )V
WAKE
( )V
DISH
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www.ti.com SLUS892B –DECEMBER 2009–REVISED SEPTEMBER 2013
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 voltage below the LOWV threshold during the 1-second discharge time. The maximum
output capacitance can be calculated as follows:
(10)
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 R2 = 500 kΩ, R1 = 100 kΩ (giving 12.6 V for voltage regulation), I
DISCH
= 8 mA,
t
DISCH
= 1 second,
(11)
Based on these calculations, no more than 2.7 mF should be allowed on the battery node for proper operation of
the battery detection circuit.
Component List for Typical System Circuit of Figure 1
PART DESIGNATOR QTY DESCRIPTION
Q1, Q2, Q3 3 P-channel MOSFET, –30 V, – 35 A, PowerPAK 1212-8, Vishay-Siliconix, Si7617DN
Q4, Q5 2 N-channel MOSFET, 30 V, 12 A, PowerPAK 1212-8, Vishay-Siliconix, Sis412DN
D1 1 Diode, dual Schottky, 30 V, 200 mA, SOT23, Fairchild, BAT54C
D2, D3, D4 3 LED diode, green, 2.1 V, 20 mA, LTST-C190GKT
R
AC
, R
SR
2 Sense resistor, 10 mΩ, 2010, Vishay-Dale, WSL2010R0100F
L1 1 Inductor, 6.8 µH, 5.5A, Vishay-Dale IHLP2525CZ
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