BQ29209-Q1 Datasheet, PDF (12/23 Pages) Texas Instruments – Voltage Protection with Automatic Cell Balance

bq29209-Q1
SLUSC62A – JUNE 2015 – REVISED MARCH 2016
9 Application and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The bq29209-Q1 is designed to be used in 2-series Li-Ion battery packs and with the option to include voltage-
based cell balancing. The number of parallel cells or the overall capacity of the battery only affects the cell
balancing circuit due to the level of potential imbalance that needs to be corrected.
9.2 Typical Applications
9.2.1 Battery Connection
Figure 9 shows the configuration for the 2-series cell battery connection with cell balancing enabled.
FUSE
CELL2
CELL1
160
1 VC 2
OUT 8
0.1 F
2 VC1
VDD 7
260
0.1 F
3 VC1_ CB CB_ EN 6
4 CD
GND 5
100
PWR PAD
0.33 F
PACK +
100
1k
Si 1406
0.1 F
PACK ±
Figure 9. 2-Series Cell Configuration
9.2.1.1 Design Requirements
For this design example, use the parameters listed in Table 1.
Table 1. Design Parameters
DESIGN PARAMETER
Input voltage range
Overvoltage Protection (OVT)
Overvoltage detection delay time
Overvoltage detection delay timer capacitor
Cell Balancing Enabled
Cell Balancing Current, ICB1 and ICB2
Cell Balancing Resistors, RCB, RCB1, RCB2 and RVD
4 V to 10 V
EXAMPLE VALUE at T_A = 25°C
4.3 V
3s
0.33 µF
Yes
10 mA
RCB = 100 Ω, RCB1 = 260 Ω, RCB2 = 160 Ω, RVD = 100 Ω
9.2.1.2 Detailed Design Procedure
The bq29209-Q1 has limited features but there are some key calculations to be made when selecting external
component values.
• Calculate the required CCD capacitor value for the voltage protection delay time. Care should be taken to
evaluate the tolerances of the capacitor and the bq29209-Q1 to ensure system specifications are met.
• Calculate the cell balancing resistor values to provide a suitable level of balancing current that will, at a
minimum, counter act an increase in imbalance during normal operation of the battery. Care should be taken
to ensure any connectivity resistance is also considered as this will also reduce the balancing current level.
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