SLUSBF2C July   2013  – August 2015

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  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  Power-On Reset
    6. 7.6  2.5-V LDO Regulator
    7. 7.7  Charger Attachment and Removal Detection
    8. 7.8  Voltage Doubler
    9. 7.9  Overvoltage Protection (OVP)
    10. 7.10 Undervoltage Protection (UVP)
    11. 7.11 Overcurrent in Discharge (OCD)
    12. 7.12 Overcurrent in Charge (OCC)
    13. 7.13 Short-Circuit in Discharge (SCD)
    14. 7.14 Low-Voltage Charging
    15. 7.15 Internal Temperature Sensor Characteristics
    16. 7.16 Internal Clock Oscillators
    17. 7.17 Integrating ADC (Coulomb Counter) Characteristics
    18. 7.18 ADC (Temperature and Cell Voltage) Characteristics
    19. 7.19 Data Flash Memory Characteristics
    20. 7.20 I2C-Compatible Interface Timing Characteristics
    21. 7.21 HDQ Communication Timing Characteristics
    22. 7.22 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Configuration
      2. 8.3.2 Fuel Gauging
      3. 8.3.3 Wake-Up Comparator
      4. 8.3.4 Battery Parameter Measurements
        1. 8.3.4.1 Charge and Discharge Counting
        2. 8.3.4.2 Voltage
        3. 8.3.4.3 Current
        4. 8.3.4.4 Auto-Calibration
        5. 8.3.4.5 Temperature
      5. 8.3.5 Communications
        1. 8.3.5.1 HDQ Single-Pin Serial Interface
        2. 8.3.5.2 HDQ Host Interruption
          1. 8.3.5.2.1 Low Battery Capacity
          2. 8.3.5.2.2 Temperature
        3. 8.3.5.3 I2C Interface
          1. 8.3.5.3.1 I2C Time Out
          2. 8.3.5.3.2 I2C Command Waiting Time
    4. 8.4 Device Functional Modes
      1. 8.4.1 NORMAL Mode
      2. 8.4.2 SLEEP Mode
      3. 8.4.3 FULLSLEEP Mode
      4. 8.4.4 Battery Protector Description
        1. 8.4.4.1 High-Side N-Channel FET Charge and Discharge FET Drive
        2. 8.4.4.2 Operating Modes
          1. 8.4.4.2.1 VIRTUAL SHUTDOWN Mode
            1. 8.4.4.2.1.1 ANALOG SHUTDOWN Mode
            2. 8.4.4.2.1.2 LOW-VOLTAGE CHARGING Mode
          2. 8.4.4.2.2 UNDERVOLTAGE FAULT Mode
          3. 8.4.4.2.3 NORMAL Mode
          4. 8.4.4.2.4 SHUTDOWN WAIT Mode
          5. 8.4.4.2.5 OVERCURRENT IN DISCHARGE (OCD) and SHORT-CIRCUIT IN DISCHARGE (SCD) FAULT Mode
          6. 8.4.4.2.6 OVERCURRENT IN CHARGE (OCC) FAULT Mode
          7. 8.4.4.2.7 OVERVOLTAGE PROTECTION (OVP) FAULT Mode
        3. 8.4.4.3 Firmware Control of Protector
      5. 8.4.5 OVERTEMPERATURE FAULT Mode
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Pack-Side, Single-Cell Li-Ion Fuel Gauge and Protector
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1  BAT Voltage Sense Input
          2. 9.2.1.2.2  SRP and SRN Current Sense Inputs
          3. 9.2.1.2.3  Sense Resistor Selection
          4. 9.2.1.2.4  TS Temperature Sense Input
          5. 9.2.1.2.5  Thermistor Selection
          6. 9.2.1.2.6  VPWR Power Supply Input Filtering
          7. 9.2.1.2.7  REG25 LDO Output Filtering
          8. 9.2.1.2.8  Communication Interface Lines
          9. 9.2.1.2.9  PACKP Voltage Sense Input
          10. 9.2.1.2.10 CHG and DSG Charge Pump Voltage Outputs
          11. 9.2.1.2.11 N-Channel FET Selection
          12. 9.2.1.2.12 Additional ESD Protection Components
        3. 9.2.1.3 Application Curves
  10. 10Power Supply Recommendations
    1. 10.1 Power Supply Decoupling
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Li-Ion Cell Connections
      2. 11.1.2 Sense Resistor Connections
      3. 11.1.3 Thermistor Connections
      4. 11.1.4 FET Connections
      5. 11.1.5 ESD Component Connections
      6. 11.1.6 High Current and Low Current Path Separation
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    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

11 Layout

11.1 Layout Guidelines

11.1.1 Li-Ion Cell Connections

For the highest voltage measurement accuracy, it is important to connect the BAT pin directly to the battery terminal PCB pad. This avoids measurement errors caused by IR drops when high charge or discharge currents are flowing. Connecting directly at the positive battery terminal with a Kelvin connection ensures the elimination of parasitic resistance between the point of measurement and the actual battery terminal. Likewise, the low current ground return for the fuel gauge and all related passive components should be star-connected precisely at the negative battery terminal. This technique minimizes measurement error due to current-induced ground offsets and also improves noise performance through prevention of ground bounce that could occur with high current and low current returns intersecting ahead of the battery ground. The bypass capacitor for this sense line needs to be placed as close as possible to the BAT input pin.

11.1.2 Sense Resistor Connections

Kelvin connections at the sense resistor are as critical as those for the battery terminals themselves. The differential traces should be connected at the inside of the sense resistor pads and not anywhere along the high current trace path in order to prevent false increases to measured current that could result when measuring between the sum of the sense resistor and trace resistance between the tap points. In addition, the routing of these leads from the sense resistor to the input filter network and finally into the SRP and SRN pins needs to be as closely matched in length as possible or an additional measurement offset may occur. It is further recommended to add copper trace or pour-based "guard rings" around the perimeter of the filter network and coulomb counter inputs to shield these sensitive pins from radiated EMI into the sense nodes. This prevents differential voltage shifts that could be interpreted as real current change to the fuel gauge. All of the filter components need to be placed as close as possible to the coulomb counter inputs pins.

11.1.3 Thermistor Connections

The thermistor sense input should include a ceramic bypass capacitor placed as close to the TS input pin as possible. The capacitor helps to filter measurements of any stray transients as the voltage bias circuit pulses periodically during temperature sensing windows.

11.1.4 FET Connections

The battery current transmission path through the FETs should be routed with large copper pours to provide the lowest resistance path possible to the system. Depending on package type, thermal vias can be placed in the package land pattern's thermal pad to reduce thermal impedance and improve heat dissipation from the package to the board, protecting the FETs during high system loading conditions. In addition, it is preferable to locate the FETs and other heat generating components away from the low power pack electronics to reduce the chance of temperature drift and associated impacts to data converter measurements. In the event of FET overheating, keeping reasonable distance between the most critical components, such as the fuel gauge, and the FETs helps to decrease the risk of thermal breakdown to the more fragile components.

11.1.5 ESD Component Connections

The ESD components included in the reference design that connect across the back-to-back FETs as well as from PACK+ to ground require trace connections that are as wide and short as possible in order to minimize loop inductance in their return path. This ensures impedance is lowest at the AC loop through the series capacitors and makes this route most attractive for ESD transients such that they are conducted away from the vulnerable low voltage, low power fuel gauge and passive components. The series resistors and Zener diodes connected to the serial communications lines should be placed as close as possible to the battery pack connector to keep large ESD currents confined to an area distant from the fuel gauge electronics. Further, all ESD components referred to ground should be single-point connected to the PACK– terminal if possible. This reduces the possibility of ESD coupling into other sensitive nodes well ahead of the PACK– ground return.

11.1.6 High Current and Low Current Path Separation

For best possible noise performance, it is important to separate the low current and high current loops to different areas of the board layout. The fuel gauge and all support components should be situated on one side of the board and tap off of the high current loop (for measurement purposes) at the sense resistor. Routing the low current ground around instead of under high current traces further helps to improve noise rejection. Finally, the high current path should be confined to a small loop from the battery, through the FETs, into the PACK connector, and back.

11.2 Layout Example

bq27741-G1 Simple_Layout.gifFigure 18. bq27741-G1 Board Layout