• State
  • Locked Locked
  • Replies 6 replies
  • Subscribers 63 subscribers
  • Views 2024 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.

BQ27426: FC bit not getting set

Martin Tramsak63
Prodigy 40 points
Part Number: BQ27426
Other Parts Discussed in Thread: EV2400, BQ24296, BQSTUDIO

Hello,

We are using BQ27426 in our system. We have completed a learning cycle but the SOC stops at 99% and never rises to 100%. We have determined that this is because FC bit is not getting set. The algorithm for determining Full charge is the default one, where FC Set% is set to -1. According to the Technical reference there are three conditions to be met to achieve full charge:

  • During two consecutive periods of 40 seconds: IRateAvg1 < Taper Rate and IRateAvg2 < Taper Rate
  • During the same periods: Accumulated change in capacity per 40-second period
  • Voltage() > Taper Voltage

I figured the second one is a typo.

Our setup:

Chemistry profile: 1202 (4200mV)
Battery capacity: 4400mAh
Taper Rate: 266
Taper Voltage: 4100mV
Charge has taper current set to 128mA and the charge voltage is set to 4200mV.

I think we successfult pass the first and last condition, but probably not the second.

Has anyone has any suggestions on how we could improve our setup or what are we doing wrong. Your help is appreciated.

  • 0
    TI__Intellectual 1840 points

    Hi,

    What is your minimum taper capacity set to ? How about your V at Chg Term ?

    Is it possible if you provide us with your gg file ?

    Thanks,

  • 0 in reply to Nabil M
    Prodigy 40 points
    Hello,

    I dont know what minimum taper capacity is since there is no reference to it in the "Technical reference" for the bq27426.

    V at chg term is chemistry profile default of 4190mV. I was unaware of this value till now i will try to reduce it. Although the voltage at the charge termination was 4205mV.

    Attached below are the gg values:

    * Texas Instruments Data Flash File
    * File created Thu May 18 08:57:56 2017
    *
    * Device Number 426
    * Firmware Version 2.02
    * Build Number not available
    * Order Number not available
    *
    * bqz Device Number 426
    * bqz Firmware Version 2.02
    * bqz Build Number 1
    *
    * Field Order: Class name, Subclass name, Parameter name, Parameter Value, Display Units
    "Configuration","Safety","Over Temp","55.0","°C"
    "Configuration","Safety","Under Temp","0","°C"
    "Configuration","Safety","Temp Hys","5.0","°C"
    "Configuration","Charge Termination","TCA Set %","99","%"
    "Configuration","Charge Termination","TCA Clear %","95","%"
    "Configuration","Charge Termination","FC Set %","-1","%"
    "Configuration","Charge Termination","FC Clear %","98","%"
    "Configuration","Charge Termination","DODatEOC Delta T","5.0","°C"
    "Configuration","Discharge","SOC1 Set Threshold","10","%"
    "Configuration","Discharge","SOC1 Clear Threshold","15","%"
    "Configuration","Discharge","SOCF Set Threshold","2","%"
    "Configuration","Discharge","SOCF Clear Threshold","5","%"
    "Configuration","Registers","OpConfig","25fa","Flag"
    "Configuration","Registers","OpConfigB","0f","Flag"
    "Configuration","Registers","OpConfigC","9f","Flag"
    "Configuration","Registers","OpConfigD","23","Flag"
    "Configuration","Power","Hibernate I","3","mA"
    "Configuration","Power","Hibernate V","2200","mV"
    "Gas Gauging","IT Cfg","OCV Wait Time","60","s"
    "Gas Gauging","IT Cfg","Ra Filter","800","Num"
    "Gas Gauging","IT Cfg","Res V Drop","32767","mV"
    "Gas Gauging","IT Cfg","Samples to Wake","240","s"
    "Gas Gauging","IT Cfg","Qmax Max Time","18000","s"
    "Gas Gauging","IT Cfg","DOD Valid Time","25","s"
    "Gas Gauging","IT Cfg","Fast Qmax Start DOD %","92","%"
    "Gas Gauging","IT Cfg","Fast Qmax End DOD %","96","%"
    "Gas Gauging","IT Cfg","Fast Qmax Start Volt Delta","125","mV"
    "Gas Gauging","IT Cfg","Fast Qmax Current Threshold","4","Hr rate"
    "Gas Gauging","IT Cfg","Fast Qmax Min Points","3","Num"
    "Gas Gauging","IT Cfg","Max Qmax Change","20","%"
    "Gas Gauging","IT Cfg","Qmax Max Delta %","10","%DCap"
    "Gas Gauging","IT Cfg","Max % Default Qmax","120","%DCap"
    "Gas Gauging","IT Cfg","Qmax Filter","96","Num"
    "Gas Gauging","IT Cfg","ResRelax Time","500","s"
    "Gas Gauging","IT Cfg","User Rate-mA","0","mA"
    "Gas Gauging","IT Cfg","User Rate-mW","0","mW"
    "Gas Gauging","IT Cfg","Max Sim Rate","1","Hr rate"
    "Gas Gauging","IT Cfg","Min Sim Rate","20","Hr rate"
    "Gas Gauging","IT Cfg","Ra Max Delta","8","4mOhm"
    "Gas Gauging","IT Cfg","Min Delta Voltage","0","mV"
    "Gas Gauging","IT Cfg","Max Delta Voltage","200","mV"
    "Gas Gauging","IT Cfg","DeltaV Max dV","100","mV"
    "Gas Gauging","IT Cfg","TermV Valid t","2","s"
    "Gas Gauging","IT Cfg","Trace Resistance","0","mOhm"
    "Gas Gauging","IT Cfg","Downstream Resistance","0","mOhm"
    "Gas Gauging","IT Cfg","Predict Ambient Time","2000","s"
    "Gas Gauging","IT Cfg","Design Energy Scale","1","Num"
    "Gas Gauging","IT Cfg","Fast Scale Load Select","3","Num"
    "Gas Gauging","IT Cfg","Chg DOD Correction Start SOC","90","Num"
    "Gas Gauging","IT Cfg","Chg DOD Correction Taper Ratio","20","Num"
    "Gas Gauging","Current Thresholds","Dsg Current Threshold","167",".1 Hr rate"
    "Gas Gauging","Current Thresholds","Chg Current Threshold","100",".1 Hr rate"
    "Gas Gauging","Current Thresholds","Quit Current","250",".1 Hr rate"
    "Gas Gauging","Current Thresholds","Dsg Relax Time","60","s"
    "Gas Gauging","Current Thresholds","Chg Relax Time","60","s"
    "Gas Gauging","Current Thresholds","Quit Relax Time","1","s"
    "Gas Gauging","Current Thresholds","Max IR Correct","400","mV"
    "Gas Gauging","State","Qmax Cell 0","16749","Num"
    "Gas Gauging","State","Update Status","00","Hex"
    "Gas Gauging","State","Reserve Cap-mAh","0","mAh"
    "Gas Gauging","State","Load Select/Mode","81","Hex"
    "Gas Gauging","State","Design Capacity","4400","mAh"
    "Gas Gauging","State","Design Energy","16300","mWh"
    "Gas Gauging","State","Terminate Voltage","3400","mV"
    "Gas Gauging","State","T Rise","20","Num"
    "Gas Gauging","State","T Time Constant","1000","s"
    "Gas Gauging","State","SOCI Delta","1","%"
    "Gas Gauging","State","Taper Rate","266",".1 Hr rate"
    "Gas Gauging","State","Sleep Current","10","mA"
    "Gas Gauging","State","Avg I Last Run","-152",".1 Hr rate"
    "Gas Gauging","State","Avg P Last Run","-157",".1 Hr rate"
    "Gas Gauging","State","Delta Voltage","1","mV"
    "Ra Tables","Ra0 RAM","Ra 0","100","Num"
    "Ra Tables","Ra0 RAM","Ra 1","60","Num"
    "Ra Tables","Ra0 RAM","Ra 2","68","Num"
    "Ra Tables","Ra0 RAM","Ra 3","92","Num"
    "Ra Tables","Ra0 RAM","Ra 4","76","Num"
    "Ra Tables","Ra0 RAM","Ra 5","64","Num"
    "Ra Tables","Ra0 RAM","Ra 6","74","Num"
    "Ra Tables","Ra0 RAM","Ra 7","62","Num"
    "Ra Tables","Ra0 RAM","Ra 8","64","Num"
    "Ra Tables","Ra0 RAM","Ra 9","70","Num"
    "Ra Tables","Ra0 RAM","Ra 10","78","Num"
    "Ra Tables","Ra0 RAM","Ra 11","78","Num"
    "Ra Tables","Ra0 RAM","Ra 12","122","Num"
    "Ra Tables","Ra0 RAM","Ra 13","230","Num"
    "Ra Tables","Ra0 RAM","Ra 14","400","Num"
    "Chemistry Info","Chem Data","Q Invalid MaxV","3809","mV"
    "Chemistry Info","Chem Data","Q Invalid MinV","3744","mV"
    "Chemistry Info","Chem Data","V at Chg Term","4190","mV"
    "Chemistry Info","Chem Data","Taper Voltage","4100","mV"
    "Calibration","Data","Board Offset","0","Counts"
    "Calibration","Data","Int Temp Offset","0","°C"
    "Calibration","Data","Ext Temp Offset","0","°C"
    "Calibration","Data","Pack V Offset","0","mV"
    "Calibration","Data","Ext a Coef 1","-11130","Num"
    "Calibration","Data","Ext a Coef 2","19142","Num"
    "Calibration","Data","Ext a Coef 3","-19262","Num"
    "Calibration","Data","Ext a Coef 4","28203","Num"
    "Calibration","Data","Ext a Coef 5","892","Num"
    "Calibration","Data","Ext b Coef 1","328","Num"
    "Calibration","Data","Ext b Coef 2","-605","Num"
    "Calibration","Data","Ext b Coef 3","-2443","Num"
    "Calibration","Data","Ext b Coef 4","4696","Num"
    "Calibration","CC Cal","CC Offset","1","Counts"
    "Calibration","CC Cal","CC Cal Temp","303.0","°K"
    "Calibration","CC Cal","CC Gain","0.2380","Num"
    "Calibration","CC Cal","CC Delta","283945.0625","Num"
    "Calibration","Current","Deadband","5","mA"
    "Security","Codes","Sealed to Unsealed","80008000","Hex"
  • 0 in reply to Martin Tramsak63
    TI__Intellectual 1840 points
    It seems like everything is fine. Is it possible for you to provide a log file of the charging profile ?
  • 0 in reply to Nabil M
    Prodigy 40 points

    Hi,

    I have the batteries at hand and the setup for the automatic learning cycle with ev2400. But I do not know how to capture log files for the charging profile. Could you give me more specifics on this.

    Today I will make another full charge cycle and will try to get FC with some values tweaked.

    Maybe I could give some more details about our setup. We are creating a tablet that will be running Android system. We are using bq27426 as the battery gage and the bq24296 as the battery charger. We wanted to have > 8000mAh of energy so we wired two 4400mAh batteries in parallel. The batteries are connected together with 0.5ohm resistor for compensation.This gives us 8800mAh of energy and nominal voltage of 3.7V. Since the gage capacity value is only valid to 8000 (as stated in datasheet and battery management studio - although I've managed to override the value to 8800 manually) we have decreased the measurement resistor to 5mOhm, thus giving us gage measured capacity of 4400mAh. We have filed an issue about the capacity problem on this forum and this was the suggested solution. As it turns out there is an application note about similar issue, so I think the resistor is not the problem.

    We had some difficulties with the learning cycle as the batteries didnt want to relax, but we have overcome this by not starting the learning cycle with batteries depleted but charged them to half full and then wait for the learning cycle to discharge them.

    Your help is appreciated
    Martin Tramsak

  • 0 in reply to Martin Tramsak63
    TI__Intellectual 1840 points
    Hi,

    BQstudios has the ability to log the battery's state. There's a "Start Log" button which will log the battery's voltage, current, SOC, temeprature, etc. For a charging profile you start the logging and begin charging the battery, you can stop logging after the taper current has been reached.

    Also, check out this document for the learning cycle, I suggest you do it manually, www.ti.com/.../slua597.pdf
  • 0 in reply to Nabil M
    Prodigy 40 points
    Hi,

    Sorry for the late response. I could not find the logging functionality of the BQStudio. I have read the application note that you suggested and tried a few more cycles. The FB bit is just not getting set.

    I have read in the datasheet that some functions are temperature dependant. We had some problems with the NTC resistors so currently the temperature is set from the host and is fixed at 25°C.

    As a last resort I tried to change the criteria for full charge detection. I tried setting FC Set % to 98% instead of -1 which means taper current monitoring. To my suprise this also does not work. The SOC and maximum charge capacity were within 2% but the FC bit is just not getting set.

    Could you give me more specifics on what constitutes as full charge, because the documentation is very scarce on this topic. I just want the criteria, because I think I covered everything and I cant get a full charge. There must be something more i guess

    Martin