BQ24105-Q1 Datasheet, PDF (18/35 Pages) Texas Instruments – SYNCHRONOUS SWITCHMODE, LI-ION AND LI-POLYMER CHARGE-MANAGEMENT IC WITH INTEGRATED POWER FETs ( bqSWITCHER™)

bq24105-Q1
SLUS953 – AUGUST 2009................................................................................................................................................................................................. www.ti.com
V_OREG
VBAT
2V/cell
No
Battery
Detected
No
Battery
Detected
Battery
Connected
Yes
Battery
Detected
I_WAKE
IBAT
- I_DISCHRG1
t_DISCHRG1
t_WAKE
t_DISCHRG1
Figure 8. Battery Detect Timing Diagram
Battery Detection Example
In order to detect a no battery condition during the discharge and wake tests, the maximum output capacitance
should not exceed the following:
a. Discharge (I_DISCHRG1 = 400 µA, t_DISCHRG1 = 1s, V_SHORT = 2V)
C_{MAX_DIS}
+
I_DISCHRG1
V_OREG *
t_DISCHRG1
V_SHORT
C_{MAX_DIS}
+
400
4.2
mA
V*
1s
2V
C_{MAX_DIS} + 182 mF
(10)
b. Wake (I_WAKE = 2 mA, t_WAKE = 0.5 s, V_OREG – V_RCH = 4.1V)
ǒ Ǔ ^{CMAX_WAKE +}
I_WAKE t_WAKE
V_OREG * V_RCH * 0 V
C_{MAX_WAKE}
+
(4.2
2 mA
V * 0.1
0.5s
V) *
0V
C_{MAX_WAKE} + 244 mF
(11)
Based on these calculations the recommended maximum output capacitance to ensure proper operation of the
battery detection scheme is 100 µF which will allow for process and temperature variations.
Figure 9 shows the battery detection scheme when a battery is inserted. Channel 3 is the output signal and
Channel 4 is the output current. The output signal switches between V_OREG and GND until a battery is inserted.
Once the battery is detected, the output current increases from 0A to 1.3A, which is the programmed charge
current for this application.
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