SLUSB20C November   2012  – November 2021


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  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: Supply Current
    6. 7.6  Digital Input and Output DC Characteristics
    7. 7.7  Power-on Reset
    8. 7.8  2.5-V LDO Regulator
    9. 7.9  Internal Clock Oscillators
    10. 7.10 ADC (Temperature and Cell Measurement) Characteristics
    11. 7.11 Integrating ADC (Coulomb Counter) Characteristics
    12. 7.12 Data Flash Memory Characteristics
    13. 7.13 I2C-Compatible Interface Communication Timing Requirements
    14. 7.14 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
    4. 8.4 Device Functional Modes
      1. 8.4.1 Power Modes
        1. BAT INSERT CHECK Mode
        2. NORMAL Mode
        3. SLEEP Mode
      2. 8.4.2 SLEEP+ Mode
      3. 8.4.3 HIBERNATE Mode
    5. 8.5 Programming
      1. 8.5.1 Standard Data Commands
      2. 8.5.2 Extended Data Commands
      3. 8.5.3 Communications
        1. I2C Interface
        2. I2C Time Out
        3. I2C Command Waiting Time
        4. I2C Clock Stretching
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. BAT Voltage Sense Input
        2. SRP and SRN Current Sense Inputs
        3. Sense Resistor Selection
        4. TS Temperature Sense Input
        5. Thermistor Selection
        6. REGIN Power Supply Input Filtering
        7. VCC LDO Output Filtering
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
    1. 10.1 Power Supply Decoupling
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Sense Resistor Connections
      2. 11.1.2 Thermistor Connections
      3. 11.1.3 High-Current and Low-Current Path Separation
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Third-Party Products Disclaimer
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Support Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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


The BQ27520-G4 fuel gauge accurately predicts the battery capacity and other operational characteristics of a single Li-based rechargeable cell. It can be interrogated by a system processor to provide cell information, such as time-to-empty (TTE), state-of-charge (SOC), and SOC interrupt signal to the host.

Information is accessed through a series of commands, called Standard Commands. Further capabilities are provided by the additional Extended Commands set. Both sets of commands, indicated by the general format Command( ), are used to read and write information contained within the device control and status registers, as well as its data flash locations. Commands are sent from system to gauge using the I2C serial communications engine, and can be executed during application development, system manufacture, or end-equipment operation.

Cell information is stored in the device in non-volatile flash memory. Many of these data flash locations are accessible during application development. They cannot generally be accessed directly during end-equipment operation. Access to these locations is achieved by either use of the companion evaluation software, through individual commands, or through a sequence of data-flash-access commands. To access a desired data flash location, the correct data flash subclass and offset must be known.

The key to the high-accuracy gas gauging prediction is Texas Instruments proprietary Impedance Track™ algorithm. This algorithm uses cell measurements, characteristics, and properties to create state-of-charge predictions that can achieve less than 1% error across a wide variety of operating conditions and over the lifetime of the battery.

The fuel gauge measures charge and discharge activity by monitoring the voltage across a small-value series sense resistor (5 mΩ to 20 mΩ, typical) located between the system VSS and the battery PACK– terminal. When a cell is attached to the device, cell impedance is learned based on cell current, cell open-circuit voltage (OCV), and cell voltage under loading conditions.

The external temperature sensing is optimized with the use of a high-accuracy negative temperature coefficient (NTC) thermistor with R25 = 10.0 kΩ ±1%. B25/85 = 3435K ± 1% (such as Semitec NTC 103AT). Alternatively, the fuel gauge can also be configured to use its internal temperature sensor or receive temperature data from the host processor. When an external thermistor is used, a 18.2-kΩ pullup resistor between the BI/TOUT and TS pins is also required. The fuel gauge uses temperature to monitor the battery-pack environment, which is used for fuel gauging and cell protection functionality.

To minimize power consumption, the device has different power modes: NORMAL, SNOOZE, SLEEP, HIBERNATE, and BAT INSERT CHECK. The fuel gauge automatically changes modes depending upon the occurrence of specific events, though a system processor can initiate some of these modes directly.

For complete operational details, see the BQ27520-G4 Technical Reference Manual (SLUUA35).


The following formatting conventions are used in this document:

Commands: italics with parentheses( ) and no breaking spaces, for example, Control( ).

Data Flash: italics, bold, and breaking spaces, for example, Design Capacity.

Register bits and flags: italics with brackets [ ], for example, [TDA]

Data flash bits: italics, bold, and brackets [ ], for example, [LED1]

Modes and states: ALL CAPITALS, for example, UNSEALED mode.