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| BQ24618 Datasheet, PDF (24/36 Pages) Texas Instruments – Stand-Alone USB-Friendly Synchronous Switch-Mode Li-Ion or Li-Polymer Battery Charger | |||
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bq24618
SLUSA55 â OCTOBER 2010
VREG
VRECH
(VWAKE)
VLOWV
(VDISH)
Battery not detected
www.ti.com
Battery
inserted
Battery detected
tLOWV_DEG
tRECH_DEG
tWAKE
Figure 21. 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:
CMAX
=
IDISCH ´ tDISCH
0.5
´
é
ê1+
R
2
ù
ú
ë R1 û
(10)
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 = 500k, R1 = 100k (giving 12.6V for voltage regulation), IDISCH = 8mA, tDISCH = 1
second,
8mA ´ 1sec
CMAX
=
0.5
´
é
êë1+
500k
100k
ù
úû
= 2.7 mF
(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
Q1, Q2, Q3
Q4, Q5
D1
D2, D3, D4
RAC, RSR
L1
QTY
2
2
1
3
2
1
DESCRIPTION
P-channel MOSFET, â30 V,â35 A, PowerPAK 1212-8, Vishay-Siliconix, Si7617DN
N-channel MOSFET, 30 V, 12 A, PowerPAK 1212-8, Vishay-Siliconix, Sis412DN
Diode, Dual Schottky, 30 V, 200 mA, SOT23, Fairchild, BAT54C
LED Diode, Green, 2.1V, 20mA, LTST-C190GKT
Sense Resistor, 10 mΩ, 2010, Vishay-Dale, WSL2010R0100F
Inductor, 6.8 µH, 5.5A, Vishay-Dale IHLP2525CZ
24
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Copyright © 2010, Texas Instruments Incorporated
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