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BQ27Z561-R1: RSOC

Part Number: BQ27Z561-R1
Other Parts Discussed in Thread: BQ27Z561

dear

Battery Charge Term Taper Current/300mA is not set to 100% RSOC, but is advanced to 707mA, resulting in 100% RSOC duration at discharge is too long, causing the overall accuracy to decline, this battery has done a lot of cycles and learning, has not been getting better, excuse me TI engineers this situation need to improve?

 thanks in advance

  • Hello Raymon,

    We recommend use a taper current of Capacity/10.

    Looking at the above log file, the voltage jumps from 3433mV to 4480mV. Are you using real cells? A full charge cycle with real cells is needed to test the taper current.

    Please provide the settings and full log file.

    Regards,
    Jose Couso

  • Hello Jose,

    Please check the GG and LOG files.

    Regards,

    Lixin Luo

    8078.rar

  • Hello Lixin,

    The Taper current value is used with the valid charge termination algorithm. Please see section 9.6 from TRM

    I suggest to try the following:

    1- Clear the CSYNC bit in the IT Gauging Configuration register. 
    2- Set the RSOCL bit in the I2C Gauging Configuration. This will tell the gauge to wait until the valid charge termination conditions are met.

    We usually recommend to set the taper current to C/10. In your case Capacity is approximately 1165 mAh. So, a taper current of ~116 mA is recommended. 

    Regards,
    Jose Couso

  • Hello Jose,

    Thank you very much for your reply, Please help comment on the following questions again:

    1. Can you comment on whether modifying CSYNC=0 will have any other impact besides the functions described in TRM?

    2. RSOCL=1, after conducting charging tests, it was found that RSOC is still only 99%, not 100%;

    3. Regarding the tap current, it is limited by the customer's charger and cannot be modified.

    Based on the 0719 GG file, I modified the Charge Term Voltage to 25mV, set the charging termination current of 280mA for the charger, and the charging completion RSOC=100. However, after about 40 minutes of standing, RemCap continued to decrease without negative current. What is the reason for this?
    The attachment is the test LOG

    JKVR-1.rar

    Best Regards,

    Lixin Luo

  • Hello Lixin,

    1- The CSYNC bit controls if the gauge should force RM to follow FCC at VCT. In some cases the Remaining capacity might be at the same level of the FCC at valid charge termination. So, if CSYNC is set, a jump in RM might be seeing. 

    2- RSOCL = 1 will hold the SOC at 99% until valid charge conditions are met. If SOC remains 99%, it means the VCT conditions were not met.

    3- This will be a good concept to follow. Note: this is for a different gauge and the BQ27z561 does not have a parameter called taper rate. 



    In regards to the Remaining capacity jump. It is very weird I will say since the gauge was at rest. This will typically happen if the cell self discharges, or a huge change in temperature, but this is not the case. The only thing I would think is RELAX_SMOOTH_OK, but it is set in your configurations. Did this happen with CSYNC = 0? What if you try toggling the CSYNC ?

    Regards,
    Jose Couso

  • Hello Jose,

    1. If CSYNC=1 is set, RM will jump, will SOC also jump? If so, the customer will not accept it.

    2. After being fully charged and left for a while, TrueRM suddenly drops to 1126, but TrueFCC does not change, resulting in the SOC dropping to 99%. Can you help me analyze why? Or what parameters need to be modified to verify, please tell me, and I will test.

    Best Regards,

    Lixin  Luo

  • Hello Lixin,

    A jump in RM will cause a jump in SOC. SOC = RM / FCC. 

    Looking at the log file again, Qmax was updated and DOD0 was updated. The gauge updates RM based on DOD. Please reference to Section 2.6 Update of DataRAM.Remaining Capacity (RM) and DataRAM.Full Charge Capacity (FCC) in the Theory and Implementation of Impedance Track Battery Fuel-Gauging Algorithm



    Have they tried setting CSYNC? Maybe this will prevent the RM from dropping to 99% as it will be set to FCC at VCT. 

    After being fully charged and left for a while, TrueRM suddenly drops to 1126, but TrueFCC does not change, resulting in the SOC dropping to 99%.

    The gauge does not use TrueRM for gauging calculations. It uses the filtered RM which is RemCap

    Regards,
    Jose Couso

  • Hello Jose,

    When will these two EoC be update?
    Question:
    As shown in the picture, the two initial values of GAUGE are 4446mV/270mA, and the accuracy measured by GAUGE can also reach about 2%. However, after several cycles of charging and discharging, this value will automatically update, Even [Current at EoC] will be updated to 0mA, and then the accuracy will also decline to about 8%. The changed value has been updated. If I manually modify the value back to 4446mV/270mmA, the accuracy of GAUGE will return to about 2%. Can you comment on the upgrading principle and impact of these two values?

    Best Regards,

    Lixin Luo

  • Hello Lixin,

    The Cell1-1 Chg Voltage at EoC and Current at EoC updates occur at the end of charge, hence, when VCT is met.

    Usually Current at EoC will update to zero when the charger terminates, but there's still enough passed charge in the 40 second window to qualify for VCT (meaning that the charger has detected full charge but not the gauge). This can lead to Current at EoC of 0mA. A recommended value is to set the gauge taper current to +/-15% of the charger taper.

    The concept here is to try that the gauge detects full charge before the charger shuts off.

    Regards,
    Jose Couso

  • Hello Jose,

    1. When the charger terminates, there should be no charging current. Why can we still detect the charging amount within 40 seconds?The charger I use is not a smart charger, and the charger will not detect gauge.

    2. I don't quite understand this +/-15%. Assuming the charging taper current is 100mA, is the gauge taper current set to 85-115mA? If the gauge taper current is set to 85mA and 85mA<100mA, it no longer meets the concept of "attempting to detect full charge before the charger is turned off".

    Regards,

    Lixin Luo

  • Hello Lixin,

    The gauge doesn't control VCT. It checks for VCT conditions (mostly voltage threshold and taper current) and once these are met, the gauge uses current, voltage and temperature measurements at this time to determine DOD for SOC = 100%.

    The gauge does not control when the charger turns off but the gauge must know the conditions when the charger turns off. This is configured for "valid charge termination". The idea is that the gauge detects a charge termination a little bit before the charger turns off. At this point, the current, by definition for most cases, is small enough that from a passed charge (and gauging) point of view, it doesn't matter if the charger continues for a few more minutes. Try setting the taper a little bit higher* (e.g. higher by15%). 

    Regards,
    Jose Couso