6 System Implementation

The Calculation shows the worst-case error of current measurement error, a physical board is also required to evaluate the real error. The BQ769x2 ground is recommended connected to the battery negative terminal. The recommended SRN and SRP pins voltage is -0.2V to 0.75V, so the trace between battery negative terminal and shunt resistor is recommended as short as enough. Otherwise, the pins voltage can exceed the recommended range during large transient current.

Before doing the accuracy test, current calibration needs to be performed to calibrate out the shunt tolerance error, coulomb counter offset and gain error. The board offset can be calibrated using the guidance of the calibration section of the BQ769x2 Calibration and OTP Programming Guide. Then gain error and shunt tolerance error can be calibrated with fix current and also following the guidance of this application note.

MSPM0 software development kit (SDK) provides the calibration demo code based on reference design High-Accuracy Battery Management Unit Reference Design for 48–1500V Energy Storage System. After installing the MSPM0 SDK and CCS, find the source code from MSPM0 SDK at:

<install_location>\ti<SDK_version>\examples\nortos\LP_MSPM0G3519\demos\bq769x2_TIDA010247

Figure 6-1 shows the TIDA-010247 pack current accuracy data under room temperature. CC3 current is used for the measurement with default 80 CC3 samples. The maximum current error is below 20mA when the discharging current is below 5A and 0.2% when the discharging current is above 5A.

Figure 6-1 Pack Current Accuracy