SLUS784E December   2007  – December 2015

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Options
  6. Pin Configuration and Functions
  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 Timing Requirements
    7. 7.7 Dissipation Ratings
    8. 7.8 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Control Logic Overview
      2. 8.3.2  Temperature Qualification (Applies Only to Versions With TS Pin Option)
      3. 8.3.3  Input Overvoltage Detection, Power Good Status Output
      4. 8.3.4  Charge Status Outputs
      5. 8.3.5  Battery Charging: Constant Current Phase
      6. 8.3.6  Charge Current Translator
      7. 8.3.7  Battery Voltage Regulation
      8. 8.3.8  Pre-Charge Timer
      9. 8.3.9  Thermal Protection Loop
      10. 8.3.10 Thermal Shutdown And Protection
      11. 8.3.11 Dynamic Timer Function
      12. 8.3.12 Charge Termination Detection and Recharge
      13. 8.3.13 Battery Absent Detection - Voltage Mode Algorithm
      14. 8.3.14 Charge Safety Timer
      15. 8.3.15 Short-Circuit Protection
      16. 8.3.16 Startup With Deeply Depleted Battery Connected
    4. 8.4 Device Functional Modes
      1. 8.4.1 Power Down
      2. 8.4.2 Sleep Mode
      3. 8.4.3 Overvoltage Lockout
      4. 8.4.4 Stand-By Mode
      5. 8.4.5 Begin Charge Mode
      6. 8.4.6 Charging Mode
      7. 8.4.7 Suspend Mode
      8. 8.4.8 LDO Mode Operation
      9. 8.4.9 State Machine Diagram
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 bq24086 and bq24088 Typical Application
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Selecting Input and Output Capacitor
          2. 9.2.1.2.2 Using Adapters With Large Output Voltage Ripple
          3. 9.2.1.2.3 Calculations
        3. 9.2.1.3 Application Curves
      2. 9.2.2 bq24085 Typical Application
        1. 9.2.2.1 Design Requirements
      3. 9.2.3 bq24087 Typical Application
        1. 9.2.3.1 Design Requirements
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Thermal Considerations
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Related Links
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

パッケージ・オプション

デバイスごとのパッケージ図は、PDF版データシートをご参照ください。

メカニカル・データ(パッケージ|ピン)
  • DRC|10
サーマルパッド・メカニカル・データ
発注情報

11 Layout

11.1 Layout Guidelines

It is important to pay special attention to the PCB layout. The following provides some guidelines:

  • To obtain optimal performance, the decoupling capacitor from IN to GND (thermal pad) and the output filter capacitors from OUT to GND (thermal pad) should be placed as close as possible to the bq2408x, with short trace runs to both IN, OUT and GND (thermal pad).
  • All low-current GND connections should be kept separate from the high-current charge or discharge paths from the battery. Use a single-point ground technique incorporating both the small signal ground path and the power ground path.
  • The high current charge paths into IN pin and from the OUT pin must be sized appropriately for the maximum charge current in order to avoid voltage drops in these traces.
  • The bq2408x family are packaged in a thermally enhanced MLP package. The package includes a thermal pad to provide an effective thermal contact between the IC and the printed circuit board (PCB); this thermal pad is also the main ground connection for the device. Connect the thermal pad to the PCB ground connection. Full PCB design guidelines for this package are provided in the application note entitled: QFN/SON PCB Attachment Application Note, SLUA271.

11.2 Layout Example

bq24085 bq24086 bq24087 bq24088 layout_ex_slus784.gif Figure 23. bq2408x PCB Layout

11.3 Thermal Considerations

The bq2408x family is packaged in a thermally enhanced MLP package. The package includes a thermal pad to provide an effective thermal contact between the IC and the printed circuit board (PCB). Full PCB design guidelines for this package are provided in the application note entitled: QFN/SON PCB Attachment Application Note, SLUA271.

The most common measure of package thermal performance is thermal impedance (θJA ) measured (or modeled) from the chip junction to the air surrounding the package surface (ambient). Use Equation 13 as the mathematical expression for θJA:

Equation 13. bq24085 bq24086 bq24087 bq24088 q_theta_ja_lus784.gif

where

  • TJ = chip junction temperature
  • TA = ambient temperature
  • P = device power dissipation

Factors that can greatly influence the measurement and calculation of θJA include:

  • Whether or not the device is board mounted
  • Trace size, composition, thickness, and geometry
  • Orientation of the device (horizontal or vertical)
  • Volume of the ambient air surrounding the device under test and airflow
  • Whether other surfaces are in close proximity to the device being tested

The device power dissipation, P, is a function of the charge rate and the voltage drop across the internal PowerFET. Use Equation 14 to calculate the device power dissipation when a battery pack is being charged:

Equation 14. P = [V(IN) – V(OUT)] × I(OUT)

Due to the charge profile of Li-Ion batteries the maximum power dissipation is typically seen at the beginning of the charge cycle when the battery voltage is at its lowest. See the charging profile, Figure 8.

If the board thermal design is not adequate the programmed fast charge rate current may not be achieved under maximum input voltage and minimum battery voltage, as the thermal loop can be active effectively reducing the charge current to avoid excessive IC junction temperature.