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BQ27426 configuration

David Azoulay
Prodigy 250 points
Other Parts Discussed in Thread: BQ27426

Hi All,

I'm using the BQ27426 in my new design. To understand what parameters i need to change i connected my BQ27426  to TI battery management studio.

Im using a li-po 110mAh 3.7V  battery.  i have a few questions:

1. As i understand from the data sheets ( and maybe im wrong) the critical parameter are:

1.chemistry -( i set it to 1202)

2. design capacity - i set it to 110mAh

3. termination voltage - 3400mV

Do i need to change more parameters to get a SOC ?

2. Does the BQ27426  preform a learning cycle automatically or i need to sand a command?

3. i have a strange problem after one cycle (charge-discharge) my SOC dosent updated. any one know what can cuse this problem?

4. im working with a micro controller a a master in my system, each time i turn off my system and on again i need to write the parameters(chemistry , design capacity etc.)   to the BQ27426  ? does the BQ27426   save his learning data or i need to save something in the micro controller  memory before turning off my system?

thanks for the help

  • 0
    TI__Guru 51466 points

    You need to select the Chemistry, the design capacity, the design energy, the terminate voltage, V at Chg Term and the taper rate.

    It will automatically learn cell characteristics. You do not have to send a command.

    If you power down the bq27426 you will have to re-configure it before it can resume gauging. You need to store the State and Ra Tables subclass before you power down the bq27426 and restore these classes after you power up.

  • 0 in reply to Dominik Hartl11
    Prodigy 250 points
    Hi Dominik
    Thanks you for your quick respond.
    Few more questions for understanding:

    1. How do i calculate the following: ( i have 110mAh battery 3.7V),
    design energy
    V at Chg Term
    taper rate.

    2. Were i can find "Sate" (the parameter that i need to save)parameter ?
    3. I need to preform one time learning cycle and crate a gold image to start with all of my batteries or i need to preform learning cycle for each one?
    3. i need to store the "Sate" and Ra Tables subclass each time im turning of my system?
    4. how can i know that my gauge finished learning cycle?
    5. what is the difference between state of charge to true state of charge?

    thanks for the help
  • 0 in reply to David Azoulay
    TI__Guru 51466 points
    design energy = design capacity * nominal voltage
    V at Chg Term = your charging voltage (depends on your charger)
    taper rate = design capacity / (0.1 * taper current)
    taper current = the current when your charger stops charging

    State subclass = see TRM, 7.4.2.3. www.ti.com/.../sluubb0.pdf

    You can create a golden image after a learning cycle and use this for all your batteries. The gauge will automatically learn over time.

    You should not turn off power to the gauge regularly. If you do, you'll have to store both the State and the Ra table subclass before you power off the gauge.

    You can check Update Status in the State subclass (see TRM 7.4.2.3.2) if the learning cycle has finished.

    SOC is a filtered state of charge and True SOC is unfiltered. True SOC may jump while SOC will be smoothed.
  • 0 in reply to Dominik Hartl11
    Prodigy 250 points

    Hi Dominik

    Thank you for your quick respond.

    Few more questions:

    1.  When you say "You should not turn off power to the gauge regularly" what do you mean by that, what is the right method to turn him off? 

    2. If I understood you correctly in need to save all the following data :

    Qmax Cell 0, Update Status, Reserve Capacity (mAh), Load Select, Load Mode,Design Capacity, Design Energy,Terminate Voltage,Thermal Rise Factor,Thermal Time Constant ,Thermal Time Constant etc. ( all the parameters that 7.4.2.3.1-7.4.2.3.15) ?

    or because most of them are default so i need only to save the:

    Chemistry, the design capacity, the design energy, the terminate voltage, V at Chg Term and the taper rate. and Ra table?

    3. My battery is permanently attached to my system i connected BIN to Vss (with 10K pull down resistor ) , do i need to send each time turning on my system a BAT_INSERT command the gauge? or just put the OpConfig [BI_PU_EN]= '1' ?

    4. i  tried to connect my fuel gas with battery management studio after its track my SOC ..when the battery discharge and get below terminate voltage i apply external power to charge the battery write the parameters that i saved ( before the battery got below terminate voltage) . but the battery management studio dosent show SOC..only after i send RESET command from the battery management studio it show SOC.

    etch time the battery get below termination voltage and then i apply charging voltage i need to send reset command to see updated SOC?( or i do something wrong)

    Dominik thank you for your help 

  • 0 in reply to David Azoulay
    TI__Guru 51466 points
    1. If the battery is not removed, you should let the gauge go into one of its power savings modes (this is automatic but can be controlled with settings like sleep current threshold). Once it is in a low power mode, it will not draw significant current from your battery.

    2. Unless your system is severely memory limited, it's simpler to just save the whole subclass. Of course, you can also just save the parameters that do change.

    3. If BIN is pulled down to GND then the gauge will detect this as an inserted battery and you do not have to send the command.

    4. You do not have to send the reset command (in fact this is not recommended and will interfere with the learning features). You must not write a new configuration each time you charge the battery from terminate voltage. The gauge will only lose its settings if it is power cycled (shutdown or disconnect).

    The correct usage is to attach the battery to your system which powers up the gauge, configure the gauge once and then do not disconnect the gauge from the battery but leave it always connected and let it go into low power states instead of disconnecting the battery. There is no need to reconfigure the gauge until it is reset (power cycle or shut-down). Just read gauging results regularly (SOC etc.).
  • 0 in reply to Dominik Hartl11
    Prodigy 250 points

    Hi Doninik

    first i want to thank you for you assist. 

    so i tried to run a learning cycle to my BQ27426  with battery management studio(=BMS) to create golden image but without a successes.

    i tried to run the learning cycle wizard on the BMS. i connected a full charge battery to my BQ27426EVM and write to my fuel gauge the following values:

    design capacity - 110 , design energy- 407 , termination voltage -3400 , taper rate - 200 (taper current 5mA), chem ID - 1202 ( 3.7V li-ion).

    and the begin of the learning cycle the BMS show a status :

    Mon Sep 05 17:07:30 IDT 2016: Learning cycle started...
    Mon Sep 05 17:07:30 IDT 2016: Start task: Discharge ( TerminateVoltage = 3400 mV )

    and ask me to connect my load . i connected my load until the battery was discharged. the BMS starting to count 5 hours for relaxation time. i waited the amount of time and then connected my battery to charger when the charging is finished im getting  the following status:

    Tue Sep 06 11:02:29 IDT 2016: Error: [QMAX_UP: Not Set]
    Tue Sep 06 11:02:29 IDT 2016: Learning cycle cancelled

    also i notice that when the battery is in relaxation time all the RAM is deleted and im getting the default values again.( when i noticed this i entered my battery parameters again)

    what im doing wrong? 

    thanks

  • 0 in reply to David Azoulay
    TI__Guru 51466 points

    >also i notice that when the battery is in relaxation time all the RAM is deleted and im getting the default values again.( when i noticed this i entered my battery parameters again)

    >what im doing wrong? 

    If the data memory is reset to default values then the gauge was reset. Did the supply voltage at the gauge drop below the minimum for the LDO (2.45V) at any time? How deep do you discharge the battery?