Datasheet

3IN
4IN
6VCC
2STAT1
19STAT2
5 PG
7 TTC
16 CE
10VSS
13NC
OUT 1
OUT 20
PGND17
PGND18
SNS15
BAT 14
ISET18
ISET29
TS12
VTSB11
V
IN
C
IN
C
OUT
R
SNS
0.1W
1.5KW 1.5KW 1.5KW
Charge
DoneAdapter
Present
7.5KW
7.5KW
9.31KW
442KW
VTSB
103AT
Battery
Pack
Pack-
Pack+
0.1 Fm
0.1 Fm
0.1 Fm
0.1 Fm
10 Fm
10 Hm
10 Fm
BQ24100
D1
R
SYS
C
TTC
L
OUT
MMBZ18VALT1
bq24100, bq24103, bq24103A
bq24104, bq24105, bq24108, bq24109
bq24113, bq24113A, bq24115
SLUS606O –JUNE 2004–REVISED MARCH 2010 www.ti.com
APPLICATION INFORMATION
Charging Battery and Powering System Without Affecting Battery Charge and Termination
Figure 18. 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.
26 Submit Documentation Feedback Copyright © 2004–2010, Texas Instruments Incorporated
Product Folder Link(s): bq24100 bq24103 bq24103A bq24104 bq24105 bq24108 bq24109 bq24113 bq24113A
bq24115