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BQ20Z655-R1: (CC) Remain Capacity Counter "jumping"

Danil Koshelev
Intellectual 320 points
Part Number: BQ20Z655-R1
Other Parts Discussed in Thread: TEST2, BQ28Z610, BQ4050

Remain Capacity "jump"

Hello,

could you answer two questions about CC of BQ20Z655-R1:

1) How to disable IT algorithm of BQ20Z655-R1, means to use only inegrated part of CC (without update Ra table and etc.)? Another TI BMS possible disable "ImpedanceTrack" by send 0x02 to "Update Staus", but BQ20Z655-R1 that procedure is fault.

2) During testing DISHARGE battery with constant current (-4 mA) I detect anomaly - Remain Capacity counter changes with a step incommensurable with the discharge current. What is the rason of this step? (data log and photo in attachment).

TEST_DSG_4mA_Test2.log

  • 0
    TI__Guru 57747 points

    Hello Danil, The load current of -4mA is too small. The gauge is operating in voltage correlation mode when conditions are close to relax mode. In this mode it updates infrequently. It looks like there was an approximately 2 percent discharge during the whole time and the gauge took at new simulation at the point in the picture. You may want to check load mode, deadband and sleep current threshold settings to analyze this further.

  • 0 in reply to Shirish
    Intellectual 320 points

    Dear Shirsh,
    please answer both my questions. I repeat here:

    1) I would like not use smart "Imedance Track" alghorithm, because I don't need correlation mode, update model and another complicate details which make debug of counting procees extremly tricky  and result of counting unpredictable . How to disable"Imedance Track" on BQ20z655 and works like a simply integrated counter? For example I was happy of quality counting CC when  disable BQ28z610  "Imedance Track" by send 0x02 to "Update Staus", but BQ20Z655-R1 that procedure is fault.

    Thank you!

  • 0 in reply to Danil Koshelev
    TI__Guru 57747 points

    Hello Danil,

    The bq20z655-R1 is not intended to be used like you have explained. CEDV gauges use coulomb counting and end of discharge voltage correction. The bq4050 is an example of CEDV gauge.

    If the bq20z655-R1is never sent the IT enable command, then impedance track algorithm is disabled. You will need to program the default senc/srec to get back to the original state where IT is not enabled.

  • 0 in reply to Shirish
    Intellectual 320 points

    "If the bq20z655-R1is never sent the IT enable command, then impedance track algorithm is disabled."
    OK, but if I didn't send "IT enable" command  - FET is not controled by FW. Is there cmd to enable FW FET control without "IT enable"?

  • 0 in reply to Danil Koshelev
    TI__Guru 57747 points

    Hello Daniel,

    The commands are listed in the TRM

    B.2 FETControl (0x46)

  • 0 in reply to Shirish
    Intellectual 320 points

    Dear Shirish,

    I think Command - B.2 FETControl (0x46) for MANUAL MOSFET control.

    After reset BQ or after disable FET -  control does not get back to  FW.

    Is that true?

  • +1 in reply to Danil Koshelev
    TI__Guru 57747 points

    Hello Danil,

    FW control of FET depends on data flash settings. It is not impacted by reset. As i mentioned before, the gauge was designed to to be used with Impedance track. If Impedance track is not enabled, then it is possible that some features may not be enabled as most features are related to the Impedance track algorithm.