Dear Expert
In the project discharger test, a sudden crash occurred during the charging and discharging of the whole machine. The investigation found that the power supply of the whole machine was stopped due to the abnormal shutdown of the MOS driving on the protection board, and the further investigation found that the abnormal MOS conduction was caused by the abnormal output driving voltage of BQ76200.
Test Step 1
Perform a charge and discharge test on the whole device or battery pack. Select individuals whose charge and discharge power is abnormal, cannot be charged, or report a charge and discharge fault.
Test step 2
For the abnormal machine, remove the protection plate, use the heat fan to set 200℃, wind speed 100, heat the BQ76200 chip for about 15S time, reinstall it to the battery pack or the whole machine, charge and discharge test, some will return to normal function, some can not return to normal, replace a BQ76200 will return to normal.
In view of the abnormal charging and discharging function of the protection plate in the previous step, the input voltage of the test BQ76200 is the normal 12V voltage, the designed capacitance of the charge pump and BAT pin is 4.7uF, and the test voltage is about 10V. The voltage of the driving output charging control pin and discharge control pin is about 0.3V (note that there are 9 or 5 driving charging NMOS, 9 or 5 driving discharge NMOS, and the CISS of MOS is about 11nF). The oscilloscope is used to measure the waveform as shown in the figure below:
