BQ24105-Q1 Datasheet, PDF (24/35 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
APPLICATION INFORMATION
Charging Battery and Powering System Without Affecting Battery Charge and Termination
R_SYS
V_IN
C_IN
1.5 KW
10 mF
1.5 KW
Adapter
Present
1.5 KW
Done
Charge
C_TTC
0.1 mF
0.1 mF
BQ24100
3 IN
OUT 1
4 IN
OUT 20
6 VCC PGND 17
2 STAT1 PGND 18
19 STAT2 SNS 15
5 PG
BAT 14
7 TTC ISET1 8
16 CE
ISET2 9
10 VSS
TS 12
13 NC
VTSB 11
L_OUT
10 mH
D1
C_OUT
MMBZ18VALT1
R_SNS
0.1W
10 mF
Battery
Pack
Pack+
Pack-
103AT
7.5 KW
7.5 KW
VTSB
9.31 KW
0.1 mF
442 KW
0.1 mF
Figure 14. Application Circuit for Charging a Battery and Powering a System Without Affecting
Termination
The bqSWITCHER was designed as a stand-alone battery charger but can be easily adapted to power a system
load, while considering a few minor issues.
Advantages:
1. The charger controller is based only on what current goes through the current-sense resistor (so precharge,
constant current, and termination all work well), and is not affected by the system load.
2. The input voltage has been converted to a usable system voltage with good efficiency from the input.
3. Extra external FETs are not needed to switch power source to the battery.
4. The TTC pin can be grounded to disable termination and keep the converter running and the battery fully
charged, or let the switcher terminate when the battery is full and then run off of the battery via the sense
resistor.
Other Issues:
1. If the system load current is large (≥ 1 A), the IR drop across the battery impedance causes the battery
voltage to drop below the refresh threshold and start a new charge. The charger would then terminate due to
low charge current. Therefore, the charger would cycle between charging and termination. If the load is
smaller, the battery would have to discharge down to the refresh threshold resulting in a much slower
cycling. Note that grounding the TTC pin keeps the converter on continuously.
2. If TTC is grounded, the battery is kept at 4.2 V (not much different than leaving a fully charged battery set
unloaded).
3. Efficiency declines 2-3% hit when discharging through the sense resistor to the system.
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