SLUSAM9E July   2011  – April 2020

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
    1.     Pin 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  Internal Power Control (Startup and Shutdown)
    7. 7.7  3.3-V Voltage Regulator
    8. 7.8  Voltage Reference
    9. 7.9  Cell Voltage Amplifier
    10. 7.10 Current Sense Amplifier
    11. 7.11 Overcurrent Comparator
    12. 7.12 Internal Temperature Measurement
    13. 7.13 Cell Balancing and Open Cell Detection
    14. 7.14 I2C Compatible Interface
    15. 7.15 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 Internal LDO Voltage Regulator
      2. 8.3.2 ADC Interface
        1. 8.3.2.1 Reference Voltage
          1. 8.3.2.1.1 Host ADC Calibration
        2. 8.3.2.2 Cell Voltage Monitoring
          1. 8.3.2.2.1 Cell Amplifier Headroom Under Extreme Cell Imbalance
          2. 8.3.2.2.2 Cell Amplifier Headroom Under BAT Voltage Drop
        3. 8.3.2.3 Current Monitoring
        4. 8.3.2.4 Overcurrent Monitoring
        5. 8.3.2.5 Temperature Monitoring
          1. 8.3.2.5.1 Internal Temperature Monitoring
      3. 8.3.3 Cell Balancing and Open Cell Detection
    4. 8.4 Device Functional Modes
      1. 8.4.1 Power Modes
        1. 8.4.1.1 POWER ON RESET (POR)
        2. 8.4.1.2 STANDBY
        3. 8.4.1.3 SLEEP
    5. 8.5 Programming
      1. 8.5.1 Host Interface
        1. 8.5.1.1 I2C Addressing
        2. 8.5.1.2 Bus Write Command to BQ76925
        3. 8.5.1.3 Bus Read Command from BQ76925 Device
    6. 8.6 Register Maps
      1. 8.6.1 Register Descriptions
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Recommended System Implementation
        1. 9.1.1.1 Voltage, Current, and Temperature Outputs
        2. 9.1.1.2 Power Management
        3. 9.1.1.3 Low Dropout (LDO) Regulator
        4. 9.1.1.4 Input Filters
        5. 9.1.1.5 Output Filters
      2. 9.1.2 Cell Balancing
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  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

8.3.2.3 Current Monitoring

Current is measured by converting current to voltage through a sense resistor connected between SENSEN and SENSEP. A positive voltage at SENSEP with respect to SENSEN indicates a discharge current is flowing, and a negative voltage indicates a charge current. The small voltage developed across the sense resistor is amplified by gain GVIOUT and output on the VIOUT pin for conversion by the Host ADC. The voltage on VIOUT is always positive and for zero current is set to 3/4 of the output range. The current sense amplifier is inverting; discharge current causes VIOUT to decrease and charge current causes VIOUT to increase. Therefore, the measurement range for discharge currents is 3 times the measurement range for charge currents.

The current-sense amplifier is preceded by a multiplexer that allows measurement of either the SENSEN or SENSEP input with respect to VSS. The Host selects the pin for measurement by writing the I_AMP_CAL bit in the CONFIG_1 register. The Host then calculates the voltage across the sense resistor by subtracting the measured voltage at SENSEN from the measured voltage at SENSEP. If the SENSEN and VSS connections are such that charge and discharge currents do not flow through the connection between them; that is, there is no voltage drop between SENSEN and VSS due to the current being measured, then the measurement of the SENSEN voltage can be regarded as a calibration step and stored by the Host for use as a pseudo-constant in the VSENSE calculation. The SENSEN voltage measurement would then only need updating when changing environmental conditions warrant.

The Host sets GVIOUT by writing the I_GAIN bit in the CONFIG_1 register. The available gains of 4 and 8 enable operation with a variety of sense-resistor values over a broad range of pack currents. The gain may be changed at any time allowing for dynamic range and resolution adjustment. The input and output ranges of the amplifier are determined by the value of the REF_SEL bit in the CONFIG_2 register. These values are shown in Table 2. Because the current amplifier is inverting, the Min column under Output Range corresponds to the Max column under Input Range. Likewise, the Max column under Output Range corresponds to the Min column under Input Range.

The actual current is calculated from the measured voltage (VIOUT) as follows. Note that VSENSE is positive when discharge current is flowing. In keeping with battery pack conventions, the sign of ISENSE is inverted so that discharge current is negative.

Equation 4. BQ76925 EQ4_tja_lusam9.gif

Table 2. Current Amplifier Configurations

REF_SEL I_GAIN Gain VIOUT (V) at ISENSE = 0
(typical)		 Input Range(1)
(mV)		 Output Range(3)
(V)		 ISENSE Range (A) at
RSENSE = 1 mΩ		 ISENSE Resolution (mA)w/10-bit ADC(2)
Min Max Min Max
0 0 4 1.0 –62.5 187.5 0.25 1.25 –62.5 – 187.5 366
0 1 8 1.0 –14 91 0.27 1.11 –14 – 91 183
1 0 4 2.0 –125 375 0.5 2.5 –125 – 375 732
1 1 8 2.0 –62.5 187.5 0.5 2.5 –62.5 – 187.5 366
(1) SENSEN or SENSEP measured with respect to VSS.
(2) Assumes 1 mΩ RSENSE and ADC reference voltage of 1.5 V and 3.0 V when REF_SEL = 0 and 1, respectively.
(3) Output range assumes typical value of VIOUT at ISENSE = 0. For non-typical values, the output range will shift accordingly.