• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Subscribers 63 subscribers
  • Views 1240 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ40Z80: The BMS is not charging or discharging the battery

Rajavarman s
Prodigy 50 points
Part Number: BQ40Z80
Other Parts Discussed in Thread: BQ25792, BQSTUDIO, EV2400

I have designed a BMS system with 4 cells in the series configuration using BQ40Z80RSMT IC. I have verified the schematic and footprints and the connections to the IC. The BMS is connected to a battery charger IC BQ25792 for charging and discharging. The charging is happening when I connect the battery externally without BMS. But both charging and discharging is not happening with the BMS IC. The battery voltage at VPACK is zero in discharging conditions. Please use the attached schematics for reference.

I tried to read voltage and current using SMBUS(Reg : 0x09 - voltage = 15235 mV and Reg : 0x0A - current = 81mA) as expected(4 cells in series mode).As there is no discharge from the IC, discharge and charge FET is in off state. I tried to toggle the Discharge FET by sending the command (0x0020).But it is not helping.

Then,I have tried to send the command (0x0022) to set the FET_EN bit,and restart the gauge ,and then check the FET_EN bit in ManufacturingStatus register.Even it is enabled, I did not see any charging or discharging from the IC. Charging and Discharging FET status in the Operation status is disabled only.

The register values (all are in Hex) which I have read are as follows :

0x54 (Operation Status register) = 00 00 6D 81

0x51 (Safety Status Register) = 00 00 40 01

0x16 (Battery Status Register) = 235

0x53 (Permanent Fail Register) = 00 00 00 00

Since SS bit is enabled, I have read the safety status register and it is showing CUV and CUVC bits as enabled which means cell under voltage protection is ON.All 7 cells are having more than 3.2 V and the CUV, CUVC thershold values (which are in 0x4BC2 and 0x4BC7) are in default values of 2500 and 2400 mV respectively.

I do not have EV2400 also for checking using BQstudio. How do I enable the charging and discharging FET in the IC?

                                                                  

  • 0
    TI__Intellectual 2146 points

    Hi Rajavarman,

    Can you read out what each of the cell voltages are? It also seems weird that that both the fully charged and fully discharged bits are both on (if I'm interpreting the battery status you wrote correctly). Can you double check that the Chem ID is accurate?

  • 0 in reply to Albert Anwar
    Prodigy 50 points

    I have read the chemical ID (0x0006) and the value I am getting is 0x1210.

    Battery status Register is giving varied values -0x235 and 0x215 .( I do not know why it is varying).

    The value of 0x0071 register( to get cell voltage) is 9e e 5f e 54 d df e e 3a 96 38 10 0 4 0 5 0 fb ff 6 0 1 0 2 0 fe ff fa ff fd ff.

    When I decode this values all the cell voltages are above 3.2 V and we are using 18650 lithium ion battery.

  • +1 in reply to Rajavarman s
    TI__Intellectual 2146 points

    Rajavarman,

    Can you read out the cell configuration register and confirm that it is properly set? It's possible that if the higher cells are enabled this could trigger the undervoltage protections because their cell voltage lines are connected to the 4th cell and would read 0V. 

  • 0 in reply to Albert Anwar
    Prodigy 50 points

    Albert, 
    I have change the cell count in cell configuration Register to 0x04 (by default it is 0x06). Now both discharging and charging is working. But to make the BMS IC work I need to change the cell configuration register( everytime for new IC), Is there any other way to modify the hardware to make the BMS IC to work in 4 cell configuration without changing the cell configuration register.

    When I try to do some implementation, the BMS IC is getting restarted ( discharging current is 3A). It is OFF for 1 sec and after that it is ON (like this it is getting restarted). Is there any register I can check or I can modify to get out of this issue.?

  • 0 in reply to Rajavarman s
    TI__Intellectual 2146 points

    Rajavarman,

    I don't believe there is a way without changing the register, unless you use 6S instead. Otherwise the gauge will think that you're using 6S and will report an error. If you need to program multiple gauges (like for mass production), we recommend using BQStudio to easily generate an .srec file that you can then program onto each of the gauges. The .srec file will contain the correct value for the cell configuration register.

    As for the gauge restarting, are you monitoring the FET status? Do you know for certain that the chip is restarting (and not just the FETs turning on and off?)? I think a good starting point would be checking the safety status register and see if any protections are getting triggered.

  • 0 in reply to Albert Anwar
    Prodigy 50 points

    Albert, 

    The FET is only getting restarted (as I did not get any discharge from IC but I can able to read the registers from the IC). 

    I have read the safety status register, I am getting the value of 00 00 40 00 which is showing like CUVC bit is enabled. 

  • 0 in reply to Rajavarman s
    TI__Intellectual 2146 points

    Rajavarman,

    Does this occur during charge as well?

    Cell undervoltage should only enable if the measured voltages of the cell is under the threshold for the specified delay or that the gauge setup is wrong. What is the undervoltage delay setting you have currently? Have you verified that the Chem ID is correct? Have you gone through the data flash settings to ensure they are all correct?