BQ76952: Thermistor reading issue

Hi Aman,

Do you have anything else connected to the thermistor pins? Capacitors are often used to help filter noise, but the value should be less than 4nF as recommended in the datasheet or it could affect the readings. If this is not the issue, can you share the register settings for these pins?

Thanks,

Matt

Hi Matt
The pins are directly connected to the Thermistor there is no capacitors in between.

Here is the list of register setting (DM) for these pins-

DM.SETTING.CONFIGURATION.CFETOFF_PIN.Byte 0x7
DM.SETTING.CONFIGURATION.TS1_PIN.Byte 0x7
DM.SETTING.CONFIGURATION.TS3_PIN.Byte 0x7
DM.SETTING.CONFIGURATION.HDQ_PIN.Byte 0x7

Here is the schematic diagram 

Thanks & Regards

Aman Sharma

Hi Aman,

The settings look okay. The only issue I see on the schematic is that the REGIN pin capacitor should ideally be 22nF, but I do not think this would explain the issue you are seeing with the thermistor measurements. Do you think there could be a problem with the device communication? Are you reading the measurements using BQStudio or with an MCU? You are using the version of the device with CRC enabled, so that should help prevent any corrupt readings.

Do you see any other strange measurements besides the thermistor readings? Have you tried on more than one device and are the thermistors well connected?

Regards,

Matt

Hi Matt,

We are using MCU to communicate with BQ76952 IC.

This issue arising once in a while at random, rest of the time all the reading including thermistor reading is ok along with all other protection functionality.
It is the reason we are unable to find out root cause of the same.

As suggested by you we shall replace 10nF with 22nF.

We have been checked for this issue and it is happening with multiple boards. 

Kindly help!

Thanks & Regards

Aman Sharma

Hi Aman,

Are you sure the MCU is correctly interpreting the CRC bytes? Can you capture this phenomenon on a logic analyzer?

Thanks,

Matt

Hi Matt,

We don't have logic analyzer but we do have DSO.

Thanks & Regards

Aman Sharma

Thanks Aman. Please share if you are able to capture these waveforms.

Hi Matt,

As you asked for waveform here are the waveforms of TS1_PIN and TS3_PIN :-

1) When BMS behaving normal and reading accurate value of thermistor.


2) When BMS is reading wrong value of thermistor(flat curves clearly says the reason for the same), CHG and DSG FET are in OFF condition but BMS is able to read individual cell voltages, Pack voltage, etc. AND there is no error in STATUS_A, STATUS_B OR STATUS_C Register.

#NOTE : BMS works ok after recovery from this issue automatically after 4 minutes(approx.).

Hi Aman,

This behavior is truly strange. Can you share your complete register settings? Are you putting the device into DEEPSLEEP mode?

Regards,

Matt

Hi Matt,

No  i'm not putting device in  DEEPSLEEP mode.

Here is the list of complete register setting (DM)

DM.SETTING.CONFIGURATION.POWER_CONFIG.Double_Byte 0x2d90
DM.SETTING.CONFIGURATION.REG12_CONFIG.Byte 0xd
DM.SETTING.CONFIGURATION.REG0_CONFIG.Byte 0x1
DM.SETTING.CONFIGURATION.HWD_REG_OPTION.Byte 0x25
DM.SETTING.CONFIGURATION.CFETOFF_PIN.Byte 0x7
DM.SETTING.CONFIGURATION.DFETOFF_PIN.Byte 0x46
DM.SETTING.CONFIGURATION.ALERT_PIN.Byte 0x2a
DM.SETTING.CONFIGURATION.TS1_PIN.Byte 0x7
DM.SETTING.CONFIGURATION.TS2_PIN.Byte 0x0
DM.SETTING.CONFIGURATION.TS3_PIN.Byte 0x7
DM.SETTING.CONFIGURATION.HDQ_PIN.Byte 0x7
DM.SETTING.CONFIGURATION.DCHG_PIN.Byte 0x2a
DM.SETTING.CONFIGURATION.DDSG_PIN.Byte 0x2a
DM.SETTING.CONFIGURATION.DA_CONFIG.Byte 0x6
DM.SETTING.CONFIGURATION.VCell_Mode 0xff
DM.SETTING.CONFIGURATION.CC3_Sample 0x0

DM.SETTING.PROTECTION.PROTECTION_CONFIG.Double_Byte 0x602
DM.SETTING.PROTECTION.ENABLED_PA.Byte 0xfc
DM.SETTING.PROTECTION.ENABLED_PB.Byte 0x37
DM.SETTING.PROTECTION.ENABLED_PC.Byte 0x80
DM.SETTING.PROTECTION.CFET_PA.Byte 0x98
DM.SETTING.PROTECTION.CFET_PB.Byte 0x15
DM.SETTING.PROTECTION.CFET_PC.Byte 0x0
DM.SETTING.PROTECTION.DFET_PA.Byte 0xe4
DM.SETTING.PROTECTION.DFET_PB.Byte 0x26
DM.SETTING.PROTECTION.DFET_PC.Byte 0x80
DM.SETTING.PROTECTION.Body_Diode_Th 0x32

DM.SETTING.ALARM.DEFAULT_ALARM_MASK.Double_Byte 0xe095
DM.SETTING.ALARM.SF_ALERT_MASK_A.Byte 0xfc
DM.SETTING.ALARM.SF_ALERT_MASK_B.Byte 0x77
DM.SETTING.ALARM.SF_ALERT_MASK_C.Byte 0x84
DM.SETTING.ALARM.PF_ALERT_MASK_A.Byte 0xdf
DM.SETTING.ALARM.PF_ALERT_MASK_B.Byte 0x9f
DM.SETTING.ALARM.PF_ALERT_MASK_C.Byte 0x78
DM.SETTING.ALARM.PF_ALERT_MASK_D.Byte 0x1

DM.SETTING.PERMANENT_FAILURE.ENABLED_PF_A.Byte 0x80
DM.SETTING.PERMANENT_FAILURE.ENABLED_PF_B.Byte 0xf
DM.SETTING.PERMANENT_FAILURE.ENABLED_PF_C.Byte 0x7e
DM.SETTING.PERMANENT_FAILURE.ENABLED_PF_D.Byte 0x0

DM.SETTING.FET.FET_OPTION.Byte 0x1f
DM.SETTING.FET.CHG_PUMP_CONTROL.Byte 0x1
DM.SETTING.FET.PreChg_Start_V 0x1f4
DM.SETTING.FET.PreChg_Stop_V 0x258
DM.SETTING.FET.PreDsg_TimeOut 0x5
DM.SETTING.FET.PreDsg_Stop_Delta 0x0

DM.SETTING.CURRENT_THRESHOLD.Dsg_Current_TH 0x0
DM.SETTING.CURRENT_THRESHOLD.Chg_Current_TH 0x0
DM.SETTING.CURRENT_THRESHOLD.OpenWire_CheckTime 0x0

DM.SETTING.MFG_STATUS_INIT.Double_Byte 0x90

DM.SETTING.CELLBALANCING_CONFIG.CB_CONFIG.Byte 0x7
DM.SETTING.CELLBALANCING_CONFIG.Min_Cell_Temp 0x0
DM.SETTING.CELLBALANCING_CONFIG.Max_Cell_Temp 0x0
DM.SETTING.CELLBALANCING_CONFIG.Max_Internal_Temp 0x0
DM.SETTING.CELLBALANCING_CONFIG.CB_Interval 0x0
DM.SETTING.CELLBALANCING_CONFIG.CB_Max_Cells 0x2
DM.SETTING.CELLBALANCING_CONFIG.CB_Min_CellV_Charge 0xcb2
DM.SETTING.CELLBALANCING_CONFIG.CB_Min_Delta_Charge 0x32
DM.SETTING.CELLBALANCING_CONFIG.CB_Stop_Delta_Charge 0x14
DM.SETTING.CELLBALANCING_CONFIG.CB_Min_CellV_Relax 0xdac
DM.SETTING.CELLBALANCING_CONFIG.CB_Min_Delta_Relax 0x32
DM.SETTING.CELLBALANCING_CONFIG.CB_Stop_Delta_Relax 0x14

_____________________________________________________________

DM.POWER.SHUTDOWN.ShutDown_CV 0x0
DM.POWER.SHUTDOWN.ShutDown_Stack_V 0x0
DM.POWER.SHUTDOWN.ShutDown_Low_V_Delay 0x0
DM.POWER.SHUTDOWN.ShutDown_Temp 0x55
DM.POWER.SHUTDOWN.ShutDown_Temp_Delay 0x0
DM.POWER.SHUTDOWN.FET_Off_Delay 0x0
DM.POWER.SHUTDOWN.ShutDown_cmd_Delay 0x0
DM.POWER.SHUTDOWN.Auto_ShutDown_Time 0x5
DM.POWER.SHUTDOWN.Ram_Fail_ShutDown_Time 0x0

DM.POWER.SLEEP.Sleep_Current 0x0
DM.POWER.SLEEP.Voltage_Sample_Time 0x0
DM.POWER.SLEEP.Wake_Comparator_Current 0x0
DM.POWER.SLEEP.Sleep_Hysteresis_Time 0x0
DM.POWER.SLEEP.Sleep_Charger_V_TH 0x0
DM.POWER.SLEEP.Sleep_Charger_Pack_TOS_Delta 0x0

DM.Config_Ram_Sign 0x0
--------------------------------------------------------------

DM.PROTECTION.CUV.Threshold 0x38
DM.PROTECTION.CUV.Delay 0x1b
DM.PROTECTION.CUV.Recovery_Hysteresis 0x3

DM.PROTECTION.COV.Threshold 0x45
DM.PROTECTION.COV.Delay 0x12d
DM.PROTECTION.COV.Recovery_Hysteresis 0x4

DM.PROTECTION.COVL.Latch_Limit 0x0
DM.PROTECTION.COVL.Counter_Dec_Delay 0x0
DM.PROTECTION.COVL.Recovery_Time 0x0

DM.PROTECTION.OCC.Threshold 0x4
DM.PROTECTION.OCC.Delay 0x7f
DM.PROTECTION.OCC.Recovery_Threshold 0x8
DM.PROTECTION.OCC.Pack_TOS_Delta 0xa

DM.PROTECTION.OCD1.Threshold 0x1
DM.PROTECTION.OCD1.Delay 0x7f

DM.PROTECTION.OCD2.Threshold 0x2
DM.PROTECTION.OCD2.Delay 0x7f

DM.PROTECTION.SCD.Threshold 0x0
DM.PROTECTION.SCD.Delay 0x1
DM.PROTECTION.SCD.Recovery_Time 0xa

DM.PROTECTION.OCD3.Threshold 0xe0c0
DM.PROTECTION.OCD3.Delay 0x1

DM.PROTECTION.OCD_Recovery_Threshold 0x9a70

DM.PROTECTION.OCDL.Latch_Limit 0x0
DM.PROTECTION.OCDL.Counter_Dec_Delay 0x0
DM.PROTECTION.OCDL.Recovery_Time 0x0
DM.PROTECTION.OCDL.Recovery_Threshold 0x9a70

DM.PROTECTION.SCDL.Latch_Limit 0x0
DM.PROTECTION.SCDL.Counter_Dec_Delay 0x0
DM.PROTECTION.SCDL.Recovery_Time 0x0
DM.PROTECTION.SCDL.Recovery_Threshold 0x9a70

DM.PROTECTION.OTC.Threshold 0x37
DM.PROTECTION.OTC.Delay 0x5
DM.PROTECTION.OTC.Recovery 0x19

DM.PROTECTION.OTD.Threshold 0x4b
DM.PROTECTION.OTD.Delay 0x5
DM.PROTECTION.OTD.Recovery 0x35

DM.PROTECTION.OTF.Threshold 0x0
DM.PROTECTION.OTF.Delay 0x0
DM.PROTECTION.OTF.Recovery 0x0

DM.PROTECTION.OTINT.Threshold 0x5a
DM.PROTECTION.OTINT.Delay 0x5
DM.PROTECTION.OTINT.Recovery 0x55

DM.PROTECTION.UTC.Threshold 0x0
DM.PROTECTION.UTC.Delay 0x5
DM.PROTECTION.UTC.Recovery 0x14

DM.PROTECTION.UTD.Threshold 0xf6
DM.PROTECTION.UTD.Delay 0x5
DM.PROTECTION.UTD.Recovery 0x0

DM.PROTECTION.UTINT.Threshold 0xf6
DM.PROTECTION.UTINT.Delay 0x5
DM.PROTECTION.UTINT.Recovery 0x0

DM.PROTECTIONRecovery_Time 0x0
DM.PROTECTION.HWD_Delay 0x0

DM.PROTECTION.LOAD_DETECT.Active_Time 0x14
DM.PROTECTION.LOAD_DETECT.Retry_Delay 0x14
DM.PROTECTION.LOAD_DETECT.TimeOut 0x0

DM.PROTECTION.PTO.Charge_Threshold 0x5
DM.PROTECTION.PTO.Delay 0x5
DM.PROTECTION.PTO.Reset 0x0

----------------------------------------------------------------

DM.PERMANENT_FAIL.CUDEP.Threshold 0x0
DM.PERMANENT_FAIL.CUDEP.Delay 0x0

DM.PERMANENT_FAIL.SUV.Threshold 0x0
DM.PERMANENT_FAIL.SUV.Delay 0x0

DM.PERMANENT_FAIL.SOV.Threshold 0x0
DM.PERMANENT_FAIL.SOV.Delay 0x0

DM.PERMANENT_FAIL.TOS.Threshold 0x0
DM.PERMANENT_FAIL.TOS.Delay 0x0

DM.PERMANENT_FAIL.SOCC.Threshold 0x0
DM.PERMANENT_FAIL.SOCC.Delay 0x0

DM.PERMANENT_FAIL.SOCD.Threshold 0x0
DM.PERMANENT_FAIL.SOCD.Delay 0x0

DM.PERMANENT_FAIL.SOT.Threshold 0x00
DM.PERMANENT_FAIL.SOT.Delay 0x00

DM.PERMANENT_FAIL.SOTF.Threshold 0x0
DM.PERMANENT_FAIL.SOTF.Delay 0x0

DM.PERMANENT_FAIL.VIMR.Check_Voltage 0
DM.PERMANENT_FAIL.VIMR.Max_Relax_Current 0
DM.PERMANENT_FAIL.VIMR.Threshold 0
DM.PERMANENT_FAIL.VIMR.Delay 0x00
DM.PERMANENT_FAIL.VIMR.Min_Relax_Current 0

DM.PERMANENT_FAIL.VIMA.Check_Voltage 0
DM.PERMANENT_FAIL.VIMA.Min_Active_Current 0
DM.PERMANENT_FAIL.VIMA.Threshold 0
DM.PERMANENT_FAIL.VIMA.Delay 0x00

DM.PERMANENT_FAIL.CFETF.Threshold 0x0
DM.PERMANENT_FAIL.CFETF.Delay 0x0

DM.PERMANENT_FAIL.DFETF.Threshold 0x0
DM.PERMANENT_FAIL.DFETF.Delay 0x0

DM.PERMANENT_FAIL.VSSF.Threshold 0x0
DM.PERMANENT_FAIL.VSSF.Delay 0x0
DM.PERMANENT_FAIL.VSSF.Delay_2LVL 0x00
DM.PERMANENT_FAIL.VSSF.Delay_LFOF 0x00
DM.PERMANENT_FAIL.VSSF.HWMX_Delay 0x00

DM.SECURITY_SETTING.Byte 0x0

DM.Unseal_Key_Step1 0
DM.Unseal_Key_Step2 0
DM.Full_Access_Key_Step1 0
DM.Full_Access_Key_Step2 0

Thanks & Regards

Aman Sharma

Hi Aman,

Can you try using the default settings and only enable set up the thermistor registers? This will help isolate whether this is a hardware issue or if there is some issue in the register settings.

I do see some issues in the register settings, but it is difficult to determine if any of these issues are related to the issue you are experiencing. Here are a few things I notice:

• DM.SETTING.CONFIGURATION.VCell_Mode 0xff   (This is not a valid setting. VC16 and VC15 must be connected to a cell) If all cells are used, this register should be written to 0x0000 or 0xFFFF
• DM.SETTING.CONFIGURATION.CC3_Sample 0x0   (There are many examples like this where I do not see the purpose of writing to this register. If you do not plan to use the CC3 measurement, I suggest leaving this parameter at the default value. Zero is outside of the allowed programmable range in BQStudio)
• I notice that the PF_EN bit is set to zero, but you are setting many bits in the PF Enabled A-D register. And then you are writing all of the PF thresholds and delays to zero (which is not valid). I suggest leaving all of these registers at default values rather than writing them without reason.
• Do not write to the Security registers if you are not using them.
• In general, only modify the register you need to. Otherwise you might be creating problems unintentionally.

Best regards,

Matt

Hi Matt,

I Modified all the settings to Default and then tried 

Here is those modified settings

// SETTING : CONFIGURATION
DM.SETTING.CONFIGURATION.POWER_CONFIG.Double_Byte = 0X2982;
DM.SETTING.CONFIGURATION.REG12_CONFIG.Byte = 0x00;
DM.SETTING.CONFIGURATION.REG0_CONFIG.Byte = 0x00;
DM.SETTING.CONFIGURATION.HWD_REG_OPTION.Byte = 0x00;
DM.SETTING.CONFIGURATION.CFETOFF_PIN.Byte = 0x07;
DM.SETTING.CONFIGURATION.DFETOFF_PIN.Byte = 0x00;
DM.SETTING.CONFIGURATION.ALERT_PIN.Byte = 0x00;
DM.SETTING.CONFIGURATION.TS1_PIN.Byte = 0x07;
DM.SETTING.CONFIGURATION.TS3_PIN.Byte = 0x07;
DM.SETTING.CONFIGURATION.HDQ_PIN.Byte = 0x07;
DM.SETTING.CONFIGURATION.DCHG_PIN.Byte = 0x00;
DM.SETTING.CONFIGURATION.DDSG_PIN.Byte = 0x00;
DM.SETTING.CONFIGURATION.DA_CONFIG.Byte = 0x05;

// SETTING : PROTECTION
DM.SETTING.PROTECTION.PROTECTION_CONFIG.Double_Byte = 0x0002;
DM.SETTING.PROTECTION.ENABLED_PA.Byte = 0x88;
DM.SETTING.PROTECTION.ENABLED_PB.Byte = 0x00;
DM.SETTING.PROTECTION.ENABLED_PC.Byte = 0x00;

DM.SETTING.PROTECTION.CFET_PA.Byte = 0x98;
DM.SETTING.PROTECTION.CFET_PB.Byte = 0xD5;
DM.SETTING.PROTECTION.CFET_PC.Byte = 0x56;

DM.SETTING.PROTECTION.DFET_PA.Byte = 0xE4;
DM.SETTING.PROTECTION.DFET_PB.Byte = 0xE6;
DM.SETTING.PROTECTION.DFET_PC.Byte = 0xE2;
DM.SETTING.PROTECTION.Body_Diode_Th = 50;

// SETTING : ALARM
DM.SETTING.ALARM.DEFAULT_ALARM_MASK.Double_Byte = 0xF800;
DM.SETTING.ALARM.SF_ALERT_MASK_A.Byte = 0xFC;
DM.SETTING.ALARM.SF_ALERT_MASK_B.Byte = 0xF7;
DM.SETTING.ALARM.SF_ALERT_MASK_C.Byte = 0xF4;
DM.SETTING.ALARM.PF_ALERT_MASK_A.Byte = 0x5F;
DM.SETTING.ALARM.PF_ALERT_MASK_B.Byte = 0x9F;
DM.SETTING.ALARM.PF_ALERT_MASK_C.Byte = 0x00;
DM.SETTING.ALARM.PF_ALERT_MASK_D.Byte = 0x00;

// SETTING : Permanent Failure
DM.SETTING.PERMANENT_FAILURE.ENABLED_PF_A.Byte = 0x00;
DM.SETTING.PERMANENT_FAILURE.ENABLED_PF_B.Byte = 0x00;
DM.SETTING.PERMANENT_FAILURE.ENABLED_PF_C.Byte = 0x07;
DM.SETTING.PERMANENT_FAILURE.ENABLED_PF_D.Byte = 0x00;

And we also tried by replacing 10nF with 22nF.

But the result is still same in both condition kindly suggest something.

Thanks & Regards

Aman Sharma

Hi Aman,

Have you configured the coefficients for the specific thermistor you are using using the https://www.ti.com/tool/BQ769X2-THERMISTOR-COEFF-CALCULATOR tool?

Best regards,

Matt

Hi Matt,

Yes I've configured the coefficients for the specific thermistor,

As I said earlier this happens once in a while.

Best Regards,

Aman Sharma

Hi Aman,

I am not sure what could cause this. Since the thermistors are far from the IC typically, could it be possible they are exposed to electromagnetic interference?

Regards,

Matt

Hi Matt,

If it is the case then it must be the constant case. 

Why it's becoming normal after 4-5 mins?

Best Regards,

Aman Sharma

Hi Aman,

I am not sure why this would happen. Are there any other conditions to note - is this occurring at room temperature, is there any switching between modes like Shutdown or DeepSleep, etc?

Regards,

Matt

Hi Matt,

No, there are no other condition appears during that case.

and yes this happens at  room temperature.

No, there are no switching happening between any modes.

Best Regards,

Aman Sharma

Hi Aman,

I notice in your original question that you try to reset the device with the TS2 pin. This will not work - can you try to toggle the RST_SHUT pin to see if it resolves the issue? It needs to be held high for less than 1 second (more than 1 second will put the device into Shutdown mode).

Thanks,

Matt