SLUSE05 December   2019 BQ78350-R1A

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
  7. 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  Electrical Characteristics: I/O
    7. 7.7  Electrical Characteristics: ADC
    8. 7.8  Electrical Characteristics: Power-On Reset
    9. 7.9  Electrical Characteristics: Oscillator
    10. 7.10 Electrical Characteristics: Data Flash Memory
    11. 7.11 Electrical Characteristics: Register Backup
    12. 7.12 SMBus Timing Specifications
    13. 7.13 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Primary (1st Level) Safety Features
      2. 8.3.2 Secondary (2nd Level) Safety Features
      3. 8.3.3 Charge Control Features
      4. 8.3.4 Fuel Gauging
      5. 8.3.5 Lifetime Data Logging
      6. 8.3.6 Authentication
      7. 8.3.7 Battery Parameter Measurements
        1. 8.3.7.1 Current and Coulomb Counting
        2. 8.3.7.2 Voltage
        3. 8.3.7.3 Temperature
    4. 8.4 Device Functional Modes
    5. 8.5 Programming
      1. 8.5.1 Physical Interface
      2. 8.5.2 SMBus Address
      3. 8.5.3 SMBus On and Off State
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Schematic
      2. 9.2.2 Design Requirements
      3. 9.2.3 Detailed Design Procedure
        1. 9.2.3.1 Measurement System
          1. 9.2.3.1.1 Cell Voltages
          2. 9.2.3.1.2 External Average Cell Voltage
          3. 9.2.3.1.3 Current
          4. 9.2.3.1.4 Temperature
        2. 9.2.3.2 Gas Gauging
        3. 9.2.3.3 Charging
          1. 9.2.3.3.1 Fast Charging Voltage
          2. 9.2.3.3.2 Fast Charging Current
          3. 9.2.3.3.3 Other Charging Modes
        4. 9.2.3.4 Protection
        5. 9.2.3.5 Peripheral Features
          1. 9.2.3.5.1 LED Display
          2. 9.2.3.5.2 SMBus Address
      4. 9.2.4 Application Performance Plots
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Power Supply Decoupling Capacitor
      2. 11.1.2 MRST Connection
      3. 11.1.3 Communication Line Protection Components
      4. 11.1.4 ESD Spark Gap
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Related Documentation
    2. 12.2 Support Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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9.2.3.1.3 Current

Current data is taken from the BQ76920 and made available through Current(). The selection of the current sense resistor connected to SRP and SRN of the BQ76920 is very important and there are several factors involved.

The aim of the sense resistor selection is to use the widest ADC input voltage range possible.

To maximize accuracy, the sense resistor value should be calculated based on the following formula:

Equation 1. RSNS(min) = V(SRP) – V(SRN) / I(max)
Where: |V(SRP) – V(SRN)| = 200 mV
I(max) = Maximum magnitude of charge of discharge current (transient or DC)

NOTE

RSNS(min) should include tolerance, temperature drift over the application temperature, and PCB layout tolerances when selecting the actual nominal resistor value.

When selecting the RSNS value, be aware that when selecting a small value, for example, 1 mΩ, then the resolution of the current measurement will be > 1 mA. In the example of RSNS = 1 mΩ, the current LSB will be 8.44 mA.

For improved accuracy, offset and gain calibration are available for this value and can be managed through the BQSTUDIO tool. The procedure for calibration is described in the BQ78350-R1A Technical Reference Manual(SLUUBD3) in the Calibration chapter.