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| BQ24600_1 Datasheet, PDF (20/31 Pages) Texas Instruments – Stand-Alone Synchronous Switch-Mode Li-Ion or Li-Polymer Battery Charger with Low Iq | |||
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bq24600
SLUS891 â FEBRUARY 2010
VREG
VRECH
(VWAKE)
VLOWV
(VDISH)
Battery not detected
www.ti.com
Battery
inserted
Battery detected
t LOWV_DEG
tRECH_DEG
t WAKE
Figure 17. 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 shown in Equation 9.
CMAX
=
IDISCH
0.5 ´
´ tDISCH
é
ê1+
R2
ù
ú
ë R1 û
(9)
Where CMAX is the maximum output capacitance, IDISCH is the discharge current, tDISCH is the discharge time, and
R2 and R1 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 = 500kâ¦, R1 = 100k⦠(giving 12.6V for voltage regulation), IDISCH = 8mA,
tDISCH = 1 second,
8mA ´ 1sec
CMAX =
0.5
´
é 500 kW ù
ëê1+ 100 kW ûú
= 2.7mF
(10)
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
Q4, Q5
D1
D2
RSR
L1
C8, C9, C12, C13
QTY
2
1
1
2
1
4
DESCRIPTION
N-channel MOSFET, 40 V, 30 A, PowerPAK SO-8, Vishay-Siliconix, SiR426DN
Diode, Dual Schottky, 30 V, 200 mA, SOT23, Fairchild, BAT54C
Schottky Diode, 40V, 5A, SMC, ON Semiconductor, MBRS540T3
Sense Resistor, 10 mâ¦, 1%, 1 W, 2010, Vishay-Dale, WSL2010R0100F
Inductor, 3.3 mH, 5.5 A, Vishay-Dale, IHLP2525CZ
Capacitor, Ceramic, 10 mF, 35 V, 10%, X7R
20
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Copyright © 2010, Texas Instruments Incorporated
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