BQ24610 Datasheet, PDF (23/33 Pages) Texas Instruments – Stand-Alone Synchronous Switch-Mode Li-Ion or Li-Polymer Battery Charger with System Power Selector and Low Iq

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V_REG
V_RECH
(V_WAKE)
V_LOWV
(V_DISH)
Battery not detected
bq24610
bq24617
SLUS892 – DECEMBER 2009
Battery
inserted
Battery detected
t_{LOWV_DEG}
t_{RECH_DEG}
t_WAKE
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:
C_MAX
=
I_DISCH ´ t_DISCH
0.5
´
é
ê¹⁺
R
2
ù
ú
ë ^R1 û
(10)
Where C_MAX is the maximum output capacitance, I_DISCH is the discharge current, t_DISCH 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), I_DISCH = 8mA, t_DISCH = 1
second,
8mA ´ 1sec
C_MAX
=
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
R_AC, R_SR
QTY
3
2
1
3
2
DESCRIPTION
P-channel MOSFET, –30 V,–35 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
Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): bq24610 bq24617
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