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BQ27750EVM-837: Leaning cycle

Nikhil Kumar86
Intellectual 275 points
Part Number: BQ27750EVM-837
Other Parts Discussed in Thread: BQ28Z610, BQ78Z100, BQSTUDIO

Hi all,

I am doing a learning cycle using bq27750EVM-837.

I am doing following steps:

1. Starting unit and applying the discharging current.

2. The battery is discharged to 0% and then I switch off the current source.

3. relax battery for 5 hours.

4. Then apply charging current by interchanging the terminals of current source and apply appositive current.

5. The unit gets charged and then relaxation of 2 hours by switching off the current source.

6. Then after that again discharging and 5 hours relaxation.

The manual I have is for bq28z610/bq78z100 and it says that

[VOK] and [RDIS] bits in the IT status() register clear once the gauge has taken an OCV reading.

If not we can use IT_Enable command to take the reading.

Is there any command in bqstudio to make sure that this reading is taken because I cannot see any IT_Enable command.

 How a golden image will help me estimating the life-cycle of the battery.

  • 0
    Intellectual 275 points
    My second issue is that the golden I have made,
    whenever I try to program it The I2C connection with the device is lost and you have to program it with original .srec file and then it gets started.
  • 0
    TI__Genius 10370 points

    Nikhil,

    Let me outline the steps that should be followed for a learn cycle and which bits should be looked at.

    1) Calibrate the Gauge

    2) Update the data flash to represent your battery.

    a. ChemID, Charging Voltage, QMax, Terminate Voltage, and others. 

    3) Send IT_enable Command (0x0021)  (Button called Gauge_EN). This will turn on [QEN] flag in [IT Status] and the [Gauge_EN] flag under [manufacturing status] register

    4) Reset Device (button called RESET). This will set [RDIS] flag in [IT Status] register

    5) Discharge battery until Terminate voltage is reached on the cell. 

    6) Rest device until [REST] flag in [IT Status] is set. This will indicate a rested open circuit voltage was read. DOD0 value should be > 14000. At this point [RDIS] will also be cleared. 

    7) Charge device until full per battery spec. 

    8) Rest device until [REST] flag in [IT Status] is set. At this point QMax will update. [Update Status] under Gas Gauging data memory tab will be updated to 05. DOD0 value should be < 1000.

    9) Discharge device until terminate voltage. During the discharge [RX] flag will toggle indicating resistance measurement are being taken. 

    10) Rest device until [REST] flag in [IT Status] is set. This will indicate a rested open circuit voltage was read. DOD0 value should be > 14000. At this point Update status should be 06 or 0E. This indicated the device is fully learned. 

    If you have any other questions please let me know

    thanks,

    Eric Vos

  • 0 in reply to Nikhil Kumar86
    TI__Genius 10370 points
    Nikhil,

    Please upgrade bqstudio versions to the test version v80 on ti.com. Use this version to export your golden srec again.

    Thanks,
    Eric Vos
  • 0 in reply to Vos
    Intellectual 275 points
    Hi Eric,
    I followed the steps all is well but the cell DOD0 is 2438
    thanks for your help
  • 0 in reply to Nikhil Kumar86
    TI__Genius 10370 points

    Nikhil,

    For the first QMax update you need to cover 90% of the capacity of the cell. After the first discharge DOD0 need to be > 14000 and after the charge < 1000. In actuality DOD_Dsg - DOD_Chg  needs to be >  14745.  If the delta is less than that you will not learn the initial QMax. 

    If DOD0 updated to 2438 that means that the battery was not charged close enough to ChgV or it did not taper the current enough. I would recommend charging further. 

    In the normal application the gauge will learn your charging method and you do not need to force this increased charge. The reason the learn cycle need 90% charge passed is to reduce the error in the initial update because resistance updated are based on this passed charge value. 

    any more questions please let me know

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Intellectual 275 points
    Hi Eric
    I tried the full charging but the DOD0 is same
    I am using a 550maH battery
    Charge termination taper current - 75mA
    Term Voltage 100mV
    Discharge threshold 60 mA and Charge threshold 55mA
    quit current 15 mA
    What I want to do is to determine the remaining life of the battery.
    Any advice on how I can proceed?
    Thanks for your help
    Kind Regards
  • 0 in reply to Nikhil Kumar86
    TI__Genius 10370 points

    Nikhil,

    Which ChemID are you using and what is the battery voltage reaching at the end of charge. DOD is determined based on the batter characterization that was done. If your cell is only being charge to 4.2V while the chemID you are using is a 4.4V ID. Then your DOD would come out too high after charge. 

    Thanks,

    Eric Vos 

  • 0 in reply to Vos
    Intellectual 275 points
    Hi Eric,
    1. The battery is at 4057mV
    2. I couldn't find the chem id in the database so I used a similar chem id.
    3. I don't know how to use the gpcc tool for chem id determination.
    Thanks for your help
  • 0 in reply to Nikhil Kumar86
    TI__Genius 10370 points

    Nikhil,

    If you read command 0x06 or hit the ChemID button on the right side of bqstudio what do you get? 

    Also is 4057mV the voltage you are charging your battery to? 

    Thanks,

    Eric Vos