BQ24650 Datasheet, PDF (19/33 Pages) Texas Instruments – Synchronous Switch-Mode Battery Charge Controller for Solar Power With Maximum Power Point Tracking

www.ti.com
V_REG
V_RECH
(V_WAKE)
V_LOWV
(V_DISCH)
Battery not detected
bq24650
SLUSA75 – JULY 2010
Battery
inserted
Battery detected
t_{LOWV_DEG}
t_{RECH_DEG}
Figure 20. Battery Detect Timing Diagram
t_WAKE
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 V_FB voltage below the LOWV threshold during the 1 second discharge time. The
maximum output capacitance can be calculated according to Equation 9:
C_MAX
=
I_DISCH
0.5 ´
´ t_DISCH
é
ê¹⁺
ë
R₂
R₁
ù
ú
û
(9)
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 = 500kΩ, R₁ = 100kΩ (giving 12.6V for voltage regulation), I_DISCH = 6mA, t_DISCH
= 1 second.
C_MAX
=
6 mA ´ 1 sec
0.5
´
é
êë¹⁺
500
100
kW
kW
ù
úû
= 2000 μF
(10)
Based on these calculations, no more than 2000 µF should be allowed on the battery node for proper operation
of the battery detection circuit.
Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): bq24650
Submit Documentation Feedback
19