BQ76952: Cell balancing dont work correctly for some battery packs

Hello Alireza,

What exactly do you mean by "cell balancing for some packs doesn't work as I expected"? Are you saying that cell balancing is not enabling at all?

Do you have a .gg file of your configuration? So I may review it. 

Although it should be able to cell balance, do you know if it can balance when Cell 16 is not in OV?

Best Regards,

Luis Hernandez Salomon

Hello Lusi,

I produced 10 battery packs (16 cells each) with a BMS. There is a microcontroller on the PCB, and I configured the BMS settings in the microcontroller. After connecting the BMS board to the batteries, I allowed them to charge to full capacity and balance.

However, I noticed that about 4 packs were not balanced after one day. Upon reading the cell balancing status for each cell in these 4 devices, I observed that cell balancing did not occur despite a difference of over 150 mV between cells.

I conducted further tests and found that cell balancing did not continue in OVP or relax mode. it only seemed to work just during charging.

Based on this observation, I can conclude that there is an issue with cell balancing in relax mode.

I can send you the configuration file (.gg )while my microcontroller configures the BMS. After configuring, I will stop the microcontroller in debugging and connect the BMS to the bqstadio.

I put my code here again.

//CELL CONFIG


#define CELL_MAX_VOLTAGE 		0x48  //3644 //mV	 devide  by 50.6
#define CELL_MIN_VOLTAGE 		0x2D //2277mv		 devide  by 50.6 0x2d



//BALANCING CONFIG


#define BALANCE_MINVOLTAGE_RELAX    3370//mv minimmum of cell voltage for balancing in relax mode
#define BALANCE_DELTASTART_RELAX    40//mv minimmum differnce between cell voltage for balancing in relax mode
#define BALANCE_DELTASTOP_RELAX     20//mv minimmum differnce between cell voltage for ignoring  in relax mode


#define BALANCE_MINVOLTAGE_CHARGE    3370//mv minimmum of cell voltage for balancing in relax mode
#define BALANCE_DELTASTART_CHARGE    40//mv minimmum differnce between cell voltage for balancing in relax mode
#define BALANCE_DELTASTOP_CHARGE     20//mv minimmum differnce between cell voltage for ignoring  in relax mode

#define BALANCE_MAX_CELL    8   //This limits how many cells may be automatically balanced in parallel 


//PRECHARGE CONFIG   
   
   
   
   
   
   
    Error_flag=CommandSubcommands(SET_CFGUPDATE);
	    if(Error_flag)
        return Error_flag;


    //////////////////////////////Power and Reg configs //////////////////////////////


    // 'Power Config' - 0x9234 = 0x2D80
    // Setting the DSLP_LDO bit allows the LDOs to remain active when the device goes into Deep Sleep mode
    // Set wake speed bits to 00 for best performance
    Error_flag=BQ769x2_SetRegister(PowerConfig, 0x2D80, 2);
    if(Error_flag)
        return Error_flag;
    // 'REG0 Config' - set REG0_EN bit to enable pre-regulator
    Error_flag=BQ769x2_SetRegister(REG0Config, 0x01, 1);
    if(Error_flag)
        return Error_flag;
//BQ769x2_SetRegister(REG0Config, 0x00, 1);
    // 'REG12 Config' - Enable REG1 with 5V output (0x0D for 3.3V, 0x0F for 5V)
    Error_flag=BQ769x2_SetRegister(REG12Config, 0x0F, 1);
    if(Error_flag)
        return Error_flag;
    //BQ769x2_SetRegister(REG12Config, 0x00 , 1);
    ////////Watch DOG
    //turn on and off reg for 7 second



    Error_flag=BQ769x2_SetRegister(HWDRegulatorOptions, 0x27, 1);
    if(Error_flag)
        return Error_flag;
    //10s with now communications will triger Watchdog
    Error_flag=BQ769x2_SetRegister(HWDDelay, 10, 2);
    if(Error_flag)
        return Error_flag;


    //////////////////////////////pin configs //////////////////////////////




    // Set DFETOFF pin to control BOTH CHG and DSG FET - 0x92FB = 0x42 (set to 0x00 to disable)
    Error_flag=BQ769x2_SetRegister(DFETOFFPinConfig, 0x42, 1);
    if(Error_flag)
        return Error_flag;

    // Set up ALERT Pin - 0x92FC = 0x2A
    // This configures the ALERT pin to drive high (REG1 voltage) when enabled.
    // The ALERT pin can be used as an interrupt to the MCU when a protection has triggered or new measurements are available
    Error_flag=BQ769x2_SetRegister(ALERTPinConfig, 0x2A, 1);
    if(Error_flag)
        return Error_flag;

    // Set TS1 to measure Cell Temperature - 0x92FD = 0x07
    Error_flag=BQ769x2_SetRegister(TS1Config, 0x07, 1);
    if(Error_flag)
        return Error_flag;
		
    Error_flag=BQ769x2_SetRegister(TS2Config, 0, 1);
    if(Error_flag)
        return Error_flag;
    // Set TS3 to measure Cell Temperature -0x92FF = 0x07
    Error_flag=BQ769x2_SetRegister(TS3Config, 0x07, 1);
    if(Error_flag)
        return Error_flag;

    // Set HDQ to measure Cell Temperature - 0x9300 = 0x07
    Error_flag=BQ769x2_SetRegister(HDQPinConfig, 0x07, 1);
    if(Error_flag)
        return Error_flag;
    // Set CFETOFF to measure Cell Temperature - 0x92FA = 0x07
    Error_flag=BQ769x2_SetRegister(CFETOFFPinConfig, 0x07, 1);
    if(Error_flag)
        return Error_flag;
    // Set DDSG to measure MOSFET Temperature - 0x9302 = 0x0F
    Error_flag=BQ769x2_SetRegister(DDSGPinConfig, 0x0F, 1);
    if(Error_flag)
        return Error_flag;
    // Set DDSG to measure MOSFET Temperature - 0x9301 = 0x0F
    Error_flag=BQ769x2_SetRegister(DCHGPinConfig, 0x0F, 1);
    if(Error_flag)
        return Error_flag;


    //////////////////////////////cell und protection configs //////////////////////////////



    // 'VCell Mode' - Enable 16 cells - 0x9304 = 0x0000; Writing 0x0000 sets the default of 16 cells
    Error_flag=BQ769x2_SetRegister(VCellMode, 0x0000, 2);
    if(Error_flag)
        return Error_flag;
    // Enable protections in 'Enabled Protections A' 0x9261 = 0xBC
    // Enables SCD (short-circuit), OCD2 (over-current in discharge), OCD1 (over-current in discharge), OCC (over-current in charge),
    // COV (over-voltage), CUV (under-voltage)
    Error_flag=BQ769x2_SetRegister(EnabledProtectionsA, 0xFC, 1);
    if(Error_flag)
        return Error_flag;
    // Enable all protections in 'Enabled Protections B' 0x9262 = 0xF7
    // Enables OTF (over-temperature FET), OTINT (internal over-temperature), OTD (over-temperature in discharge),
    // OTC (over-temperature in charge), UTINT (internal under-temperature), UTD (under-temperature in discharge), UTC (under-temperature in charge)
    Error_flag=BQ769x2_SetRegister(EnabledProtectionsB, 0xF7, 1);
    if(Error_flag)
        return Error_flag;
		
		// Enable Precharge Timeout (PTO)
		Error_flag=BQ769x2_SetRegister(EnabledProtectionsC, 0x04, 1);
    if(Error_flag)
        return Error_flag;
    // 'Default Alarm Mask' - 0x..82 Enables the FullScan and ADScan bits, default value = 0xF800
    Error_flag=BQ769x2_SetRegister(DefaultAlarmMask, 0xF882, 2);
    if(Error_flag)
        return Error_flag;


    //////////////////////////////cell balancing configs //////////////////////////////



    // Set up Cell Balancing Configuration - 0x9335 = 0x03   -  Automated balancing while in Relax or Charge modes
    // Also see "Cell Balancing with BQ769x2 Battery Monitors" document on ti.com
    Error_flag=BQ769x2_SetRegister(BalancingConfiguration, 0x03, 1);
    if(Error_flag)
        return Error_flag;
    //Relax mode
    Error_flag=BQ769x2_SetRegister(CellBalanceMinCellVRelax, BALANCE_MINVOLTAGE_RELAX, 2);
    if(Error_flag)
        return Error_flag;
    Error_flag=BQ769x2_SetRegister(CellBalanceMinDeltaRelax, BALANCE_DELTASTART_RELAX, 1);
    if(Error_flag)
        return Error_flag;
    Error_flag=BQ769x2_SetRegister(CellBalanceStopDeltaRelax, BALANCE_DELTASTOP_RELAX, 1);
    if(Error_flag)
        return Error_flag;

    //Charge mode
    Error_flag=BQ769x2_SetRegister(CellBalanceMinCellVCharge, BALANCE_MINVOLTAGE_CHARGE, 2);
    if(Error_flag)
        return Error_flag;
    Error_flag=BQ769x2_SetRegister(CellBalanceMinDeltaCharge, BALANCE_DELTASTART_CHARGE, 1);
    if(Error_flag)
        return Error_flag;
    Error_flag= BQ769x2_SetRegister(CellBalanceStopDeltaCharge,  BALANCE_DELTASTOP_CHARGE, 1);
    if(Error_flag)
        return Error_flag;
    //Number of cell that we want to balancing in same time
    Error_flag=BQ769x2_SetRegister(CellBalanceMaxCells,  BALANCE_MAX_CELL, 1);
    if(Error_flag)
        return Error_flag;
    Error_flag=BQ769x2_SetRegister(CellBalanceInterval,5, 1);
    if(Error_flag)
        return Error_flag;


    //////////////////////////////precharge  configs //////////////////////////////

    // start pre charge from 500mv pro cell until PRECHARGE_STOP_VOLTAGE pro cell
    Error_flag=BQ769x2_SetRegister(PrechargeStartVoltage,  PRECHARGE_START_VOLTAGE, 2);
    if(Error_flag)
        return Error_flag;
    Error_flag=BQ769x2_SetRegister(PrechargeStopVoltage,  PRECHARGE_STOP_VOLTAGE, 2);
    if(Error_flag)
        return Error_flag;
		
    Error_flag=BQ769x2_SetRegister(PTODelay,  18000, 2); //5 uhr precharge timeout (s)
    if(Error_flag)
        return Error_flag;




    //////////////////////////////predischarge  configs //////////////////////////////

		 //Enable predischarge seq
	  Error_flag=BQ769x2_SetRegister(FETOptions,  0x1D,1);
    if(Error_flag)
        return Error_flag;

		
		 //set pre discharge timeout to 2.50 sec  = 250 * 10 ms
    Error_flag=BQ769x2_SetRegister(PredischargeTimeout,  250,1);
    if(Error_flag)
        return Error_flag;

    


    //////////////////////////////shutdown protect configs //////////////////////////////

 		if(fail_status.OTP_FAIL==0)
		{
    Error_flag=BQ769x2_SetRegister(ShutdownStackVoltage, (PACK_SHUTDOWN_VOLTAGE/10), 2);
    if(Error_flag)
        return Error_flag;

		Error_flag=BQ769x2_SetRegister(LowVShutdownDelay, 10, 1);
    if(Error_flag)
        return Error_flag;

		}
    //////////////////////////////temp protection configs //////////////////////////////

	Error_flag=BQ769x2_SetRegister(OTCThreshold, 45, 1);//charge over temp  10-45 according datasheet
		    if(Error_flag)
        return Error_flag;
					
	Error_flag=BQ769x2_SetRegister(OTCDelay, 2, 1);
				    if(Error_flag)
        return Error_flag;
							
	Error_flag=BQ769x2_SetRegister(OTCRecovery, 40, 1);
    if(Error_flag)
        return Error_flag;
		
		
		Error_flag=BQ769x2_SetRegister(OTDThreshold, 55, 1);//discharge over temp  -20-55 according datasheet
		    if(Error_flag)
        return Error_flag;
				
	Error_flag=BQ769x2_SetRegister(OTDDelay, 2, 1);
				    if(Error_flag)
        return Error_flag;
						
	Error_flag=BQ769x2_SetRegister(OTDRecovery, 50, 1);
    if(Error_flag)
        return Error_flag;		

//mosfet over temp is defult 80 and bms internal temp is 85
		
		
		
    //////////////////////////////voltage and currnet protection configs //////////////////////////////




    // Set up CUV (under-voltage) Threshold - 0x9275 = 0x31 (2479 mV)
    // CUV Threshold is this value multiplied by 50.6mV
    Error_flag=BQ769x2_SetRegister(CUVThreshold, CELL_MIN_VOLTAGE, 1);
    if(Error_flag)
        return Error_flag;
		

 	 Error_flag=BQ769x2_SetRegister(CUVRecoveryHysteresis, 2 , 1);	//that mean 2*50.6 mv more =101.2mv
    if(Error_flag)
        return Error_flag;				
		
		
 	 Error_flag=BQ769x2_SetRegister(BodyDiodeThreshold, 200 , 2);	//set threshold to turn on dsg or cs mosfet after cuv or cov 400ma
    if(Error_flag)
        return Error_flag;			
		
		

    // Set up COV (over-voltage) Threshold - 0x9278 = 0x48 3643 mV)
    // COV Threshold is this value multiplied by 50.6mV
    Error_flag=BQ769x2_SetRegister(COVThreshold, CELL_MAX_VOLTAGE, 1);
    if(Error_flag)
        return Error_flag;




    // Set up OCC (over-current in charge) Threshold - 0x9280 = 0x05 (14 mV = 14A across 1mOhm sense resistor) Units in 2mV
    Error_flag=BQ769x2_SetRegister(OCCThreshold, (PACK_MAX_CHARGE_CURRENT/2), 1);
    if(Error_flag)
        return Error_flag;
		
		 Error_flag=BQ769x2_SetRegister(OCCRecoveryThreshold, 300, 2);
    if(Error_flag)
        return Error_flag;

    // Set up OCD1 Threshold - 0x9282 = 0x0A (20 mV = 20A across 1mOhm sense resistor) units of 2mV
    Error_flag=BQ769x2_SetRegister(OCD1Threshold, (PACK_MAX_DISCHARGE_CURRENT/2), 1);
    if(Error_flag)
        return Error_flag;
		
	    // Set up OCD1 delay 100 *3.3ms = 3.3s
	    Error_flag=BQ769x2_SetRegister(OCD1Delay,120, 1);
    if(Error_flag)
        return Error_flag;	
		
		
		
	    // Set up OCD2 Threshold - 0x9282 = 0x0A (20 mV = 20A across 1mOhm sense resistor) units of 2mV
    Error_flag=BQ769x2_SetRegister(OCD2Threshold, ((PACK_MAX_DISCHARGE_CURRENT+80)/2), 1);
    if(Error_flag)
        return Error_flag;	
		
		 Error_flag=BQ769x2_SetRegister(OCD2Delay,20, 1);
    if(Error_flag)
        return Error_flag;		
		
		//set threshold to turn off ocd alert , ma
		Error_flag=BQ769x2_SetRegister(OCDRecoveryThreshold, 10, 2);
    if(Error_flag)
        return Error_flag;
		
			//set threshold to turn off ocdl alert , ma	
		Error_flag=BQ769x2_SetRegister(OCDLRecoveryThreshold, 10, 2);
    if(Error_flag)
        return Error_flag;

    // Set up SCD Threshold - 0x9286 = 11 (300 mV = 200A across 1mOhm sense resistor)  0x05=100mV
    Error_flag=BQ769x2_SetRegister(SCDThreshold, 11 , 1);
    if(Error_flag)
        return Error_flag;

    // Set up SCD Delay - 0x9287 = 0x0B (150 us) Enabled with a delay of (value - 1) * 15 µs; min value of 1
    Error_flag=BQ769x2_SetRegister(SCDDelay, 0x0B, 1);
    if(Error_flag)
        return Error_flag;

    // Set up SCDL Latch Limit to 1 to set SCD recovery only with load removal 0x9295 = 0x01
    // If this is not set, then SCD will recover based on time (SCD Recovery Time parameter).
    Error_flag=BQ769x2_SetRegister(SCDLLatchLimit, 0x01, 1);
    if(Error_flag)
        return Error_flag;


    Error_flag=BQ769x2_SetRegister(MfgStatusInit, 0x0080, 2);
    if(Error_flag)
        return Error_flag;

		if((device_profile.calibration_current!=0)&&(device_profile.calibration_current!=-1))
		{
			    Error_flag=BQ769x2_SetRegister(BoardOffset, (device_profile.calibration_current*10) , 2);
    if(Error_flag)
        return Error_flag;	
		}

		
		
		
    Error_flag=CommandSubcommands(EXIT_CFGUPDATE);
    if(Error_flag)
        return Error_flag;
		
		
    return OK;

best regards

Alireza

Hello Alireza,

The .gg file would be great to look over! So send whenever you get it on-hand.

Now, I see you have the Settings:Cell Balancing Config:Balancing Configuration register set to 0x03. This would mean that charging is allowed in relax or in charge. However, I also see that the Settings:Cell Balancing Config:Balancing Configuration[CB_SLEEP] is set to 0, this would mean that balancing is not allowed in SLEEP mode. 

Do you have SLEEP enabled during these tests? If you disable SLEEP with the SLEEP_DISABLE() command, are you able to balance?

Best Regards,

Luis Hernandez Salomon

Hello Lusi,

I have exported the .gg file

and here is the situation of the registers:

I didn't find the problem until now.  SLEEP_DISABLE()  also didn't change any things.

best regards

Alireza

  balancing_problem.gg.csv

Hello Alireza,

Your cell voltages do not meet the cell balancing requirements in that image, did you try getting a condition for cell balance there?

The SLEEP_DISABLE() would disable SLEEP mode, so I think it should balance there if the conditions for balancing are met.

I see in relax mode you have a Minimum Cell Voltage of 3370-mV to start balancing. And a minimum cell voltage delta of 40-mV. So I'd expect balancing would start at roughly 3.41-V or so.

Best Regards,

Luis Hernandez Salomon