SBASA31B November   2020  – November 2021 ADS131B04-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 Timing Diagrams
    9. 6.9 Typical Characteristics
  7. 7 Parameter Measurement Information
    1. 7.1 Noise Measurements
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Input ESD Protection Circuitry
      2. 8.3.2  Input Multiplexer
      3. 8.3.3  Programmable Gain Amplifier (PGA)
      4. 8.3.4  Voltage Reference
      5. 8.3.5  Internal Test Signals
      6. 8.3.6  Clocking
        1. 8.3.6.1 External Clock Using CLKIN Pin
        2. 8.3.6.2 Internal Oscillator
      7. 8.3.7  ΔΣ Modulator
      8. 8.3.8  Digital Filter
        1. 8.3.8.1 Digital Filter Implementation
          1. 8.3.8.1.1 Fast-Settling Filter
          2. 8.3.8.1.2 SINC3 and SINC3 + SINC1 Filter
        2. 8.3.8.2 Digital Filter Characteristic
      9. 8.3.9  Calibration Registers
      10. 8.3.10 Register Map CRC
    4. 8.4 Device Functional Modes
      1. 8.4.1 Power-Up and Reset
        1. 8.4.1.1 Power-On Reset
        2. 8.4.1.2 SYNC/RESET Pin
        3. 8.4.1.3 RESET Command
      2. 8.4.2 Fast Start-Up Behavior
      3. 8.4.3 Conversion Modes
        1. 8.4.3.1 Continuous-Conversion Mode
        2. 8.4.3.2 Global-Chop Mode
      4. 8.4.4 Power Modes
      5. 8.4.5 Standby Mode
      6. 8.4.6 Synchronization
    5. 8.5 Programming
      1. 8.5.1 Serial Interface
        1. 8.5.1.1  Chip Select (CS)
        2. 8.5.1.2  Serial Data Clock (SCLK)
        3. 8.5.1.3  Serial Data Input (DIN)
        4. 8.5.1.4  Serial Data Output (DOUT)
        5. 8.5.1.5  Data Ready (DRDY)
        6. 8.5.1.6  SPI Communication Frames
        7. 8.5.1.7  SPI Communication Words
        8. 8.5.1.8  Short SPI Frames
        9. 8.5.1.9  Communication Cyclic Redundancy Check (CRC)
        10. 8.5.1.10 SPI Timeout
      2. 8.5.2 ADC Conversion Data Format
      3. 8.5.3 Commands
        1. 8.5.3.1 NULL (0000 0000 0000 0000)
        2. 8.5.3.2 RESET (0000 0000 0001 0001)
        3. 8.5.3.3 STANDBY (0000 0000 0010 0010)
        4. 8.5.3.4 WAKEUP (0000 0000 0011 0011)
        5. 8.5.3.5 LOCK (0000 0101 0101 0101)
        6. 8.5.3.6 UNLOCK (0000 0110 0110 0110)
        7. 8.5.3.7 RREG (101a aaaa annn nnnn)
          1. 8.5.3.7.1 Reading a Single Register
          2. 8.5.3.7.2 Reading Multiple Registers
        8. 8.5.3.8 WREG (011a aaaa annn nnnn)
      4. 8.5.4 Collecting Data for the First Time or After a Pause in Data Collection
    6. 8.6 Register Map
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Troubleshooting
      2. 9.1.2 Unused Inputs and Outputs
      3. 9.1.3 Antialias Filter
      4. 9.1.4 Minimum Interface Connections
      5. 9.1.5 Multiple Device Configuration
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Current Shunt Measurement
        2. 9.2.2.2 Battery Pack Voltage Measurement
        3. 9.2.2.3 Shunt Temperature Measurement
        4. 9.2.2.4 Auxiliary Analog Supply Voltage Measurement
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
    1. 10.1 CAP Pin Capacitor Requirement
    2. 10.2 Power-Supply Sequencing
    3. 10.3 Power-Supply Decoupling
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

9.2.2.1 Current Shunt Measurement

In a typical BMS, the current through the shunt resistor must be measured in both directions for charging and discharging the battery pack. In an overcurrent or short-circuit condition, the current can be as high as IBAT_MAX = ±5 kA in this example application. Therefore, the maximum voltage drop across the shunt is up to VSHUNT =
RSHUNT × IBAT_MAX = 35 μΩ × ±4 kA = ±140 mV.

In order to measure this shunt voltage, channel 2 of the ADS131B04-Q1 is configured for gain = 8, which allows differential voltage measurements of VIN2 = VAIN2P – VAIN2N = ±VREF / 8 = ±1.2 V / 8 = ±150 mV. The integrated charge pump in the device allows voltage measurements 300 mV below AGND for gains of 4 and higher while using a unipolar analog power supply. This bipolar voltage measurement capability is important because one side of the shunt is connected to the same GND potential as the AGND pin of the ADS131B04-Q1, which means that the absolute voltage that the device must measure is up to 140 mV below AGND.

To enable fast overcurrent detection within 1 ms while providing high accuracy and resolution, the ADS131B04-Q1 is operated at 4 kSPS (OSR = 1024, high-resolution mode) using global-chop mode. Global-chop mode enables measurements with minimal offset error over temperature and time. The conversion time using these settings is 0.754 ms according to Equation 6. The input-referred noise is approximately 1.29 μVRMS / √2 = 0.91 μVRMS following the explanations in the Section 7.1 section. Thus, currents as small as 0.91 μVRMS / 35 μΩ = 26 mA can be resolved. The resolution can be further improved by averaging the conversion results over a longer period of time in the microcontroller that interfaces with the ADS131B04-Q1.

Channel 2 is selected for the shunt measurement on purpose because this channel generally shows the best offset error and offset drift with global-chop mode enabled across all four ADC channels. Of all the measurements, the offset performance is the most critical for the shunt measurement in a typical BMS.