SLUSA52C September 2010 – March 2016
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.
The bq2920x 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.
Figure 9 shows the configuration for the 2-series cell battery connection with cell balancing enabled.
For this design example, use the parameters listed in Table 1.
|DESIGN PARAMETER||EXAMPLE VALUE at TA = 25°C|
|Input voltage range||4 V to 10 V|
|Overvoltage Protection (OVT)||4.35 V|
|Overvoltage detection delay time||3 s|
|Overvoltage detection delay timer capacitor||0.33 µF|
|Cell Balancing Enabled||Yes|
|Cell Balancing Current, ICB1 and ICB2||10 mA|
|Cell Balancing Resistors, RCB, RCB1, RCB2 and RVD||RCB = 100 Ω, RCB1 = 260 Ω, RCB2 = 160 Ω, RVD = 100 Ω|
The bq2920x has limited features but there are some key calculations to be made when selecting external component values.
Higher cell balancing currents can be supported by means of a simple external network, as shown in Figure 11.
RCLAMP ensures that both Q1 and Q2 remain off when balancing is disabled, and should be sized above 2 kΩ to prevent excessive internal device current when the balancing network is activated. RCB_EXT determines the value of the balancing current, and is dependent on the voltage of the balanced cell, as follows: