SLUSA52C September   2010  – March 2016

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Options
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Recommended Cell Balancing Configurations
    7. 7.7 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
      1. 8.1.1 Voltage Protection
      2. 8.1.2 Cell Balancing
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Protection (OUT) Timing
      2. 8.3.2 Cell Voltage > VPROTECT
      3. 8.3.3 Cell Connection Sequence
      4. 8.3.4 Cell Balance Enable Control
      5. 8.3.5 Cell Balance Configuration
      6. 8.3.6 Cell Imbalance Auto-Detection (Via Cell Voltage)
      7. 8.3.7 Customer Test Mode
      8. 8.3.8 Test Conditions
    4. 8.4 Device Functional Modes
      1. 8.4.1 NORMAL Mode
      2. 8.4.2 PROTECTION Mode
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Battery Connection
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
        3. 9.2.1.3 Application Curve
    3. 9.3 System Example
      1. 9.3.1 External Cell Balancing
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Related Links
    2. 12.2 Community Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • DRB|8
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9 Application and Implementation

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 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.

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.

bq29200 bq29209 Apps-Diag.gif 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 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

9.2.1.2 Detailed Design Procedure

The bq2920x 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 bq2920x 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.

9.2.1.3 Application Curve

bq29200 bq29209 C001_SLUSA52.png Figure 10. Average VPROTECT Accuracy (VOA) Across Operation Temperature

9.3 System Example

9.3.1 External Cell Balancing

Higher cell balancing currents can be supported by means of a simple external network, as shown in Figure 11.

bq29200 bq29209 Ext_Cell_Balancing.gif Figure 11. External Cell Balancing Configuration

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:

bq29200 bq29209 ExtCell_Equation.gif