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BQ79606A-Q1: Voltage protector when balancing

Part Number: BQ79606A-Q1


I have 3 BMS designs with BQ79606 for LFP packs: 12S / 15S / 16S

These 3 BMS have the same problem: when balancing occurs, the voltage protector (3.8V) is triggered.

Without balancing, everything is fine (the comparators work)

The datasheet says that voltage protection is automatically disable when balance is active.


The register configuration:

WriteReg(0, OV_THRESH, 0x44, 1, FRMWRT_ALL_NR); //3,7V

WriteReg(0, COMP_DG, 0x0F, 1, FRMWRT_ALL_NR);   //set 500us comparators deglitch timer

WriteReg(0, OVUV_CTRL, 0x3F, 1, FRMWRT_SGL_NR); //enable all cell Over voltage/Under voltage

WriteReg(1, OVUV_CTRL, 0x3F, 1, FRMWRT_SGL_NR); //enable all cell Over voltage/Under voltage

WriteReg(2, OVUV_CTRL, 0x07, 1, FRMWRT_SGL_NR); //enable all cell Over voltage/Under voltage

WriteReg(0, CONTROL2, 0x14, 1, FRMWRT_ALL_NR); //TSREF enable, Enables the OV/UV comparators

WriteReg(0, CONTROL2, 0x17, 1, FRMWRT_ALL_NR); //CELL_ADC_GO = 1, TSREF enable, AUX_ADC_GO, OVUV_EN

WriteReg(0, CB_CONFIG, 0xAA, 1, FRMWRT_ALL_NR); // duty cycle of 10s, continue to balancing (no of thermal shutdown), Odds then even cells

WriteReg(0, CB_DONE_THRESHOLD, 0x20, 1, FRMWRT_ALL_NR);//disable CD_DONE


To activate balancing, the software writes:

WriteReg(0, CB_CELL2_CTRL, 0x8A, 1, FRMWRT_SGL_NR);          //10s cycle for cell balancing

WriteReg(0, CONTROL2, 0x36, 1, FRMWRT_ALL_NR);    //BAL_GO = 1, TSREF, AUX_ADC_GO, OTUT_EN = 1, OVUV_EN


When balancing occurs at cell 2, the voltage across CB1 – CB0 increases (4.5V) and I can see :

  • with debugging (CAN bus) that the OV_FAULT register is set
  • the fault pin is cleared

Why is the comparator triggered? Should firmware disable comparator before enabling balancing?