SLUSFB5A June   2024  – April 2025 BQ41Z50

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
    1. 4.1 Pin Equivalent Diagrams
  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  Power Supply Control
    7. 5.7  Low Dropout Regulators
    8. 5.8  Internal Oscillators
    9. 5.9  Voltage References
    10. 5.10 Current Wake Detector
    11. 5.11 VC0, VC1, VC2, VC3, VC4, PACK
    12. 5.12 Cell Balancing Support
    13. 5.13 SMBD, SMBC
    14. 5.14 PRES/SHUTDN, DISP
    15. 5.15 ALERT
    16. 5.16 LEDCNTLA, LEDCNTLB, LEDCNTLC
    17. 5.17 Coulomb Counter
    18. 5.18 Coulomb Counter Digital Filter (CC1)
    19. 5.19 Current Measurement Digital Filter (CC2)
    20. 5.20 Analog-to-Digital Converter
    21. 5.21 ADC Digital Filter
    22. 5.22 CHG, DSG High-side NFET Drivers
    23. 5.23 Precharge (PCHG) FET Drive
    24. 5.24 FUSE Drive
    25. 5.25 Internal Temperature Sensor
    26. 5.26 TS1, TS2, TS3, TS4
    27. 5.27 Flash Memory
    28. 5.28 OT, SCD, OCC, OCD1, OCD2 Protection Thresholds (SCOMP)
    29. 5.29 OT, SCD, OCC, OCD1, OCD2 Protection Timing (SCOMP)
    30. 5.30 GPIO1, GPIO2, GPIO3, GPIO4, GPIO5, GPIO6, GPIO7
    31. 5.31 Elliptical Curve Cryptography (ECC)
    32. 5.32 SMBus Interface Timing
    33. 5.33 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 Primary (1st Level) Safety Features
      2. 6.3.2 Secondary (2nd Level) Safety Features
      3. 6.3.3 Charge Control Features
      4. 6.3.4 Gas Gauging
      5. 6.3.5 Lifetime Data Logging Features
      6. 6.3.6 Authentication
      7. 6.3.7 Configuration
        1. 6.3.7.1 Oscillator Function
        2. 6.3.7.2 Real Time Clock
        3. 6.3.7.3 System Present Operation
        4. 6.3.7.4 Emergency Shutdown
        5. 6.3.7.5 2-Series, 3-Series, or 4-Series Cell Configuration
        6. 6.3.7.6 Cell Balancing
        7. 6.3.7.7 LED Display
      8. 6.3.8 Battery Parameter Measurements
        1. 6.3.8.1 Charge and Discharge Counting
        2. 6.3.8.2 Voltage
        3. 6.3.8.3 Current
        4. 6.3.8.4 Temperature
        5. 6.3.8.5 Communications
          1. 6.3.8.5.1 SMBus On and Off State
          2. 6.3.8.5.2 SBS Commands
    4. 6.4 Device Functional Modes
  8. 7 Applications and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Applications
      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 Chemical Fuse
          3. 7.2.2.1.3 Lithium-Ion Cell Connections
          4. 7.2.2.1.4 Sense Resistor
          5. 7.2.2.1.5 ESD Mitigation
        2. 7.2.2.2 Gas Gauge Circuit
          1. 7.2.2.2.1 Coulomb-Counting Interface
          2. 7.2.2.2.2 Low-dropout Regulators (LDOs)
            1. 7.2.2.2.2.1 REG18
            2. 7.2.2.2.2.2 REG135
          3. 7.2.2.2.3 System Present
          4. 7.2.2.2.4 SMBus Communication
          5. 7.2.2.2.5 FUSE Circuitry
        3. 7.2.2.3 Secondary-Current Protection
          1. 7.2.2.3.1 Cell and Battery Inputs
          2. 7.2.2.3.2 External Cell Balancing
          3. 7.2.2.3.3 PACK and FET Control
          4. 7.2.2.3.4 Temperature Measurement
          5. 7.2.2.3.5 LEDs
      3. 7.2.3 Application Curves
    3. 7.3 Configuring Device Firmware
  9. 8 Power Supply Recommendations
  10. 9 Layout
    1. 9.1 Layout Guidelines
      1. 9.1.1 Protector FET Bypass and Pack Terminal Bypass Capacitors
      2. 9.1.2 ESD Spark Gap
    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 Receiving Notification of Documentation Updates
    4. 10.4 Support Resources
    5. 10.5 Trademarks
    6. 10.6 Electrostatic Discharge Caution
    7. 10.7 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

9.1 Layout Guidelines

A battery fuel gauge circuit board is a challenging environment due to the fundamental incompatibility of high-current traces and ultra-low current semiconductor devices. The best way to protect against unwanted trace-to-trace coupling is with a component placement, such as that shown in Figure 9-1, where the high-current section is on the opposite side of the board from the electronic devices. Clearly this is not possible in many situations due to mechanical constraints. Still, every attempt should be made to route high-current traces away from signal traces, which enter the BQ41Z50 directly. IC references and registers can be disturbed and in rare cases damaged due to magnetic and capacitive coupling from the high-current path. Note that during surge current and ESD events, the high-current traces appear inductive and can couple unwanted noise into sensitive nodes of the gas gauge electronics, as illustrated in Figure 9-2.

BQ41Z50 Separating High- and Low-Current Sections Provides an Advantage in Noise ImmunityFigure 9-1 Separating High- and Low-Current Sections Provides an Advantage in Noise Immunity
BQ41Z50 Avoid Close Spacing Between High-Current and Low-Level Signal LinesFigure 9-2 Avoid Close Spacing Between High-Current and Low-Level Signal Lines

Kelvin voltage sensing is extremely important in order to accurately measure current and top and bottom cell voltages. Place all filter components as close as possible to the device. Route the traces from the sense resistor in parallel to the filter circuit. Adding a ground plane around the filter network can add additional noise immunity. Figure 9-3 and Figure 9-4 demonstrates correct kelvin current sensing.

BQ41Z50 Sensing Resistor PCB LayoutFigure 9-3 Sensing Resistor PCB Layout
BQ41Z50 Sense Resistor, Ground Shield, and Filter Circuit LayoutFigure 9-4 Sense Resistor, Ground Shield, and Filter Circuit Layout

Some suggestions to improve the system level resiliancy to ESD were tested and improved the performance significantly:

  • Add ground planes—Ground planes are used to add distributed capacitance to the layout itself, this reduces the voltage seen on the pins of the IC. For multilayer PCBs, separate the signal layers with a ground plane. Add more layers to improve the ESD system level performance.

  • Keep the VCC cap populated and as close as possible to the gauge IC.