SLUSG59 February   2026 BQ27Z855

ADVANCE INFORMATION  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configurations and Functions
  6. 5 Specifications
    1. 5.1  Absolute Maximum Ratings
    2. 5.2  ESD Ratings
    3. 5.3  Recommended Operating Conditions
    4. 5.4  Supply Current
    5. 5.5  1.8V LDO Regulator (REG18)
    6. 5.6  Low Frequency Oscillator (LFO)
    7. 5.7  High Frequency Oscillator (HFO)
    8. 5.8  PACK Clamp (PACK_CLAMP)
    9. 5.9  Analog-to-Digital Converter (VADC)
    10. 5.10 Coulomb Counter (CCADC)
    11. 5.11 Coulomb Counter Digital Filter (CC1)
    12. 5.12 Current Measurement Digital Filter (CC2)
    13. 5.13 Charge Current Measurement Digital Filter (CC3)
    14. 5.14 Wake-up Comparator (I-WAKE)
    15. 5.15 Internal Temperature Sensor (INT_TEMP)
    16. 5.16 Thermistor Measurement Support
    17. 5.17 Hardware-based Protection (SCOMP) Thresholds (OVP, UVP, OCC, OCD, SCD)
    18. 5.18 Hardware-based Protections (SCOMP) Timing (OVP, UVP, OCC, OCD, SCD)
    19. 5.19 Current Limiter
    20. 5.20 CHG, DSG NFET Drivers
    21. 5.21 Zero-volt Charging (ZVCHG)
    22. 5.22 General Purpose Input-Outputs (INT)
    23. 5.23 I2C Interface I/O (SDA, SCL)
    24. 5.24 I2C Interface Timing
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1  BQ27Z855 Processor
      2. 6.3.2  Battery Parameter Measurements
        1. 6.3.2.1 Analog-to-Digital Converter (VADC)
        2. 6.3.2.2 VADC Multiplexer
        3. 6.3.2.3 Coulomb Counter (CCADC) and Digital Filter (CC1)
        4. 6.3.2.4 Internal Temperature Sensor (INT_TEMP)
        5. 6.3.2.5 External Temperature Sensor Support
      3. 6.3.3  Power Supply Control
      4. 6.3.4  ENAB Pin
      5. 6.3.5  I2C Bus Communication Interface
      6. 6.3.6  Low Frequency Oscillator (LFO)
      7. 6.3.7  High Frequency Oscillator (HFO)
      8. 6.3.8  Real Time Clock (RTC)
      9. 6.3.9  1.8V Low Dropout Regulator (REG18)
      10. 6.3.10 FET Drivers (CHG, DSG)
        1. 6.3.10.1 Charge (CHG) FET Driver
        2. 6.3.10.2 Discharge (DSG) FET Driver
      11. 6.3.11 Zero-volt Charging (ZVCHG)
      12. 6.3.12 Integrated Protections
        1. 6.3.12.1 Hardware-based Protections
          1. 6.3.12.1.1 Overvoltage Protection (OVP)
          2. 6.3.12.1.2 Undervoltage Protection (UVP)
          3. 6.3.12.1.3 Overcurrent in Charge Protection (OCC)
          4. 6.3.12.1.4 Overcurrent in Discharge Protection (OCD)
          5. 6.3.12.1.5 Short Circuit Current in Discharge Protection (SCD)
          6. 6.3.12.1.6 Wake-up Comparator (I-WAKE)
        2. 6.3.12.2 Firmware-based Protections
          1. 6.3.12.2.1 Primary Level Protection Features
          2. 6.3.12.2.2 Secondary Level Protection Features
      13. 6.3.13 Gas Gauging
      14. 6.3.14 Advanced Battery Algorithms
        1. 6.3.14.1 Si-anode Chemistry Support
        2. 6.3.14.2 Internal Short Indication (ISI)
        3. 6.3.14.3 Battery Swelling Detection (BSD)
      15. 6.3.15 Integrated Current Limiter and Charge Control Features
        1. 6.3.15.1 Integrated Current Limiter
          1. 6.3.15.1.1 CHG FET State Machine
          2. 6.3.15.1.2 Linear Mode
            1. 6.3.15.1.2.1 Battery Charging Process
            2. 6.3.15.1.2.2 Zero-volt Charge (ZVCHG)
            3. 6.3.15.1.2.3 Precharge (PCHG)
            4. 6.3.15.1.2.4 Fast Charge (CC)
            5. 6.3.15.1.2.5 Taper-charge (CV)
            6. 6.3.15.1.2.6 Charge Termination (VCT)
            7. 6.3.15.1.2.7 Step-charging Profile Support
          3. 6.3.15.1.3 MINSYS Mode
          4. 6.3.15.1.4 Battery Supplement Mode
        2. 6.3.15.2 Interaction with a Smart Charger
      16. 6.3.16 Ideal Diode Mode
      17. 6.3.17 Lifetime Data Logging Features
      18. 6.3.18 Authentication
        1. 6.3.18.1 ECC ECDSA Authentication
        2. 6.3.18.2 SHA-256 Authentication
      19. 6.3.19 Over the Air (OTA) Field Updater
      20. 6.3.20 Configuration
        1. 6.3.20.1 Cell Voltage Measurements
        2. 6.3.20.2 Coulomb Counting
        3. 6.3.20.3 Temperature Measurements
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application Schematics
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 High-Current Path
          1. 7.2.2.1.1 Protection FETs
          2. 7.2.2.1.2 Battery Cell Connections
          3. 7.2.2.1.3 Sense Resistor
          4. 7.2.2.1.4 ESD Mitigation
        2. 7.2.2.2 Gas Gauge Circuit
          1. 7.2.2.2.1 Cell Voltage Measurement Interface
          2. 7.2.2.2.2 Coulomb Counter Interface
          3. 7.2.2.2.3 Temperature Measurement
          4. 7.2.2.2.4 1.8V Low Dropout Regulator (REG18)
          5. 7.2.2.2.5 I2C Communication (SDA, SCL)
          6. 7.2.2.2.6 Interrupt to Host Interface (INT)
        3. 7.2.2.3 Current Limiter Circuit
          1. 7.2.2.3.1 Protection FETs and Compatibility with BQ27Z855
          2. 7.2.2.3.2 CP Control Logic and Capacitor
          3. 7.2.2.3.3 Voltage-based Feedback Interface
          4. 7.2.2.3.4 Current-based Feedback Interface
            1. 7.2.2.3.4.1 Sense Resistor Impact on Current-based Feedback
            2. 7.2.2.3.4.2 Sense Resistor Impact on CHG FET State Transitions
          5. 7.2.2.3.5 BAT-PACK Dedicated Voltage Comparator (DCOMP)
            1. 7.2.2.3.5.1 Impact of Sense Resistor Configuration on DCOMP Sensing
          6. 7.2.2.3.6 System-level Recommendations
        4. 7.2.2.4 Co-design with BQ27Z746 and BQ27Z758
          1. 7.2.2.4.1 Footprint Compatibility and Equivalent Pins
          2. 7.2.2.4.2 Co-layout Example
  9. 8 Power Supply Recommendations
  10. 9 Layout
    1. 9.1 Layout Guidelines
  11. 10Device and Documentation Support
    1. 10.1 Third-Party Products Disclaimer
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
    3. 10.3 Trademarks
    4. 10.4 Electrostatic Discharge Caution
    5. 10.5 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information
    1.     PACKAGE OPTION ADDENDUM
    2. 12.1 Tape and Reel Information
    3. 12.2 Mechanical Data
7.2.2.2.1 Cell Voltage Measurement Interface

The cell input is conditioned with a bypass capacitor (CBAT) with a recommended typical value of 1μF connected between the device's BAT pin and GND reference (VSS). This capacitor acts to filter unwanted voltage transients and provides some ESD protection during cell connect. The BQ27Z855 device uses the BAT pin as the device's power source, so this bypass capacitor connected between the device's BAT pin and VSS also acts to filter unwanted voltage ripples at the input of the device's internal 1.8V LDO.

A 0Ω resistor (RBAT) can be placed between the postivie terminal of the cell and device BAT pin if needed to split the net names, but a higher resistor value is not recommended to ensure the proper linear charger functionality and entry in and out of supplement mode. See Section 7.2.2.3.2 and Section 7.2.2.3.3 for more details.

Also, as described in Figure 7-4, the top node of the cell must be sensed at the battery connections with a Kelvin connection to prevent voltage sensing errors caused by a voltage drop from the PCB copper trace.

BQ27Z855 Cell Voltage Measurement Input Figure 7-6 Cell Voltage Measurement Input