SLUSG59A February   2026  – November 2026 BQ27Z855

PRODUCTION DATA  

  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  Thermal Information
    5. 5.5  Supply Current
    6. 5.6  1.8V LDO Regulator (REG18)
    7. 5.7  Low Frequency Oscillator (LFO)
    8. 5.8  High Frequency Oscillator (HFO)
    9. 5.9  PACK Clamp (PACK_CLAMP)
    10. 5.10 Analog-to-Digital Converter (VADC)
    11. 5.11 Coulomb Counter (CCADC)
    12. 5.12 Coulomb Counter Digital Filter (CC1)
    13. 5.13 Current Measurement Digital Filter (CC2)
    14. 5.14 Charge Current Measurement Digital Filter (CC3)
    15. 5.15 Wake-up Comparator (I-WAKE)
    16. 5.16 Internal Temperature Sensor (INT_TEMP)
    17. 5.17 Thermistor Measurement Support
    18. 5.18 Hardware-based Protection (SCOMP) Thresholds (OVP, UVP, OCC, OCD, SCD)
    19. 5.19 Hardware-based Protections (SCOMP) Timing (OVP, UVP, OCC, OCD, SCD)
    20. 5.20 Linear Battery Charger
    21. 5.21 CHG, DSG NFET Drivers
    22. 5.22 Zero-Volt Charging (ZVCHG)
    23. 5.23 General Purpose Input-Outputs (INT)
    24. 5.24 I2C Interface I/O (SDA, SCL)
    25. 5.25 I2C Interface Timing
    26. 5.26 Typical Characteristics
  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
      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 Control
          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
      3. 7.2.3 Application Curves
  9. 8 Power Supply Recommendations
  10. 9 Layout
    1. 9.1 Layout Guidelines
    2. 9.2 Layout Example
  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

6.3.11 Zero-volt Charging (ZVCHG)

ZVCHG (0-V charging) is a special function that allows charging a severely depleted battery. The BQ27Z855 device has ZVCHG enabled with no inhibit. This means a severely depleted battery with a voltage as low as 0V can be charged.

With a voltage applied at the PACK+ terminal of the battery pack, the BQ27Z855 device conducts ZVCHG current within the device via an internal path from the PACK pin to the BAT pin. The resistor between the PACK+ terminal of the battery pack and the PACK pin of the device current limits the ZVCHG current (IZVCHG) through the device effectively setting what ZVCHG current the battery charges at or is used to wake a secondary protector. IZVCHG is limited to IZVCHG(MAX) as stated in the Zero-volt Charging Specifications table.

If VBAT is below the entry threshold set by device firmware to qualify the battery as being in a ZVCHG state, the device disables the CHG FET and can start zero-volt charging once a voltage is applied at the PACK+ terminal of the battery pack. CHG FET will be in ideal diode state as long as DSG FET is enabled, otherwise both FETs are disabled. Once the battery is charged enough and VBAT reaches the exit threshold programmed in device firmware, the device stops conducting zero-volt charging and assesses if the both FETs can be turned ON.

Both FETs are disabled while the device is in a ZVCHG state and VBAT is below the POR threshold (VPOR_TH - VPOR_HYS).

The ZVCHG path through the device is always enabled when VBAT is below the device POR threshold.  Once the device is above the POR threshold, the ZVCHG path will be enabled when Voltage() is below the ZVCHG Exit Threshold.

If the ZVCHG function is unused, a larger resistance value of RPACK can be used.

CAUTION:

Some battery providers do not recommend charging a depleted (self-discharged) battery. Consult the battery supplier to determine whether to have the ZVCHG battery charger function.

For safety purposes, the BQ27Z855 is specifically designed to be used in battery systems with at least 1 additional protector unit with an inhibitied zero-volt charging feature. This prevents unwanted battery self-discharge to severely low voltage levels or initiating charging at very low battery voltages that can cause irreversible damage to the battery.

BQ27Z855 Zero-volt Charging PathFigure 6-2 Zero-volt Charging Path