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
7.2.2.3.4.1 Sense Resistor Impact on Current-based Feedback

As stated in Section 7.2.2.2.2, choosing a sense resistor (RSENSE) value presents a tradeoff between the sense resistor value and the current resolution reported by the device's Coulomb counter for gauging calculations. This tradeoff is also present when the device's current limiter is enabled and impacts the current resolution the device senses and regulates charging current at.

This tradeoff is detailed as follows:

  • A higher sense resistor value yields a lower current resolution and can be more appropriate for applications using lower battery capacities and or lower charging currents
  • A lower sense resistor value yields a higher current resolution and can be more appropriate for applications using higher battery capacities and or higher charging currents

Using a combination of a particular sense resistor value and particular charging currents impacts the charging current resolution of the device since the device's battery charging functionality scales based on the sense resistor value.

In addition to the resolution, the sense resistor value also impacts the minimum charging current setting to achieve particular charging current accuracy. As a general guideline to achieve charging current accuracy of ±10%, the charging current settings programmed in device data flash is not recommended to be below the minimum values given in Table 7-2. Charging current settings below the recommended range when using a particular sense resistor value can still be programmed, but charging current regulated by the device may not be as accurate as ±10%. The charging current programmed in device data flash should also not exceed ICHG(MAX) as specified in the Current Limiter Specifications table. The combination of sense resistor value and charging current settings should be considered carefully then.

The sense resistor value's impact on charging current resolution and accuracy should be considered when programming the fast charge and precharge current settings in device data flash.

Table 7-2 provides guidance on how the sense resistor value impacts the charging current (ICHG) resolution and recommended range of the device:

Table 7-2 ICHG Resolution and Accuracy Versus RSENSE
0.5mΩ 1mΩ 2mΩ 5mΩ 10mΩ 20mΩ 50mΩ 100mΩ
ICHG Resolution (mA) 29.30 14.65 7.32 2.93 1.46 0.73 0.29 0.15
Minimum ICHG Setting (mA)(1) 925 463 231 93 46 23 9 5
(1) General guideline on minimum ICHG setting to achieve ±10% ICHG accuracy. Programming lower currents in device data flash may not be as accurate.

A lower termiantion current (ITERM) setting below the recommended ICHG range is allowed, but should not exceed ITERM(MAX) as specified in the Current Limiter Specifications table. Similar to the above general guideline to achieve ±10% ICHG accuracy, the ITERM setting programmed in device data flash is not recommended to be below the minimum values given in Table 7-3 to achieve ±10% ITERM accuracy. ITERM settings below the recommended range when using a particular sense resistor value can still be programmed, but the ITERM value detected by the device may not be as accurate as ±10%.

Table 7-3 provides guidance on how the sense resistor value impacts the ITERM resolution and recommended range of the device:

Table 7-3 ITERM Resolution and Accuracy Versus RSENSE
0.5mΩ 1mΩ 2mΩ 5mΩ 10mΩ 20mΩ 50mΩ 100mΩ
ITERM Resolution (mA) 1.85 0.92 0.46 0.18 0.09 0.05 0.02 0.01
Minimum ITERM Setting (mA)(1) 55 28 14 6 3 1 1(2) 1(2)
(1) General guideline on minimum ITERM setting to achieve ±10% ITERM accuracy. Programming lower currents in device data flash may not be as accurate.
(2) There is no recommended minimum ITERM value to consider with this RSENSE to achieve ±10% ITERM accuracy. The programmable step size and minimum nonzero setting for Charge Term Taper Current in device data flash is 1mA.