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BQ27520-G4: Performing Learning Cycle for BQ27520-G4

Part Number: BQ27520-G4
Other Parts Discussed in Thread: GPCCHEM

Hi Everyone,

We are working on one product which is Battery operated AI Camera and we are using BQ27520-G4 Fuel gauge to monitor the Battery. We want to perform Learning cycle for our battery. Attaching the battery datasheet for your reference. Please find my queries below.

1) Is the CHEM ID of the attached battery(Cell:- 18650 Samsung 30Q 3000mah cell) is present in the BQ27520-G4 latest firmware? 

2) As per SLUA902, We need to do calibration for 20 Boards minimum and then to average it and write the data in the other board. Do we need to do calibration in any specific operating condition like temperature range? What factors need to take care for calibration?

3) How to perform Learning cycle and what factors needs to take care while doing learning cycle?

Along with above queries if anything specific we need to take care while performing learning cycle please let us know.

Thank you in advance for help.

DNK 18650 30Q 1S1P Battery pack datasheet final one.pdf

  • Hi Madhav,

    1. The GPCCHEM tool found below can assist you in checking if your battery is in the current chemistry. If it is not, this tool will show you the closest chemistry to your battery. 

    2. What temperature range are you planning using this device in? The basic calibration instructions can be found in Section 8 of this document below: 

    3. The instructions to complete the learning cycle can be found below. 


    Anthony Baldino

  • Hi Anthony Baldino

    Thank you for your reply.

    I started the learning cycle but After charging cycle FC bit not becoming high. In my case we have battery with BMS system. In BMS discharge protection is present which will cutoff battery supply if it goes below 2.8V so When I tries to discharge my battery fully it voltage cuts off and so fuel gauge also stops.

    So I have below queries.

    1) If my voltage cuts down and when again I charge the battery, Is my learning cycle again continues from there or it will fails? If fails what is the better way to discharge battery fully without cutoff.

    2) Full avilable capacity is coming 2572mAh but as per battery it is 3000mAh. Why it is not updating when I charge or discharge the battery fully.

  • Hi Madhav,

    Is it possible for you to tell us what protector is being used that is causing this?


    Anthony Baldino

  • Hi Anthony,

    Please find the attached datasheet of BMS.

    LZ-1860-1S3M 3.7V 7A BMS.pdf

  • Hi Madhav,

    Can you tell me what the terminal voltage is for this battery?

    Typically this value will be around 3V for most batteries, however if it is below 2.8V for this battery, is there a way to disable the protector so the learning cycle can complete?


    Anthony Baldino

  • Hi Anthony

    For Battery cell terminal voltage is 2.5V, but for battery protector it is 2.8V. Attaching the cell datasheet for your reference.

    We can remove the protector circuit, but what is the Ideal way to do with protector circuit or without protector circuit because in our end product protector circuit will be present.

    Also which parameters affect if we not discharge battery to 100% in battery cycle?


  • Hi Madhav,

    The parameters such as State of Charge, State of Health, and the accuracy of the Impedance Track algorithm can be affected by not discharging the battery to its terminal voltage during the learning cycle.

    Can you please tell me if this application is designed to stop at 2.8V or 2.5V?

    If designed to stop at 2.8V, we believe that the protector will need to be disabled for the learning cycle to complete.


    Anthony Baldino

  • Hi Anthony,

    The application is designed to stop at 2.8V.

    We will remove protection circuit now and start the learning cycle, Please check the below setups and let me know if anything wrong.

    1) Plug the Full charge battery and Calibrate the Fuel Gauge for all parameters.

    2) Send IT_ENABLE command, then RESET command and then UNSEAL_FULL_ACCESS command.

    3) Discharge battery by C/5 to C/10 rate. (In our case Battery capacity is 3000mAh so 3000/5 = 600mA.) So Discharge at rate of 600mA

    4) Discharge upto 2.8V. (Here I have doubt. We need to discharge by checking battery voltage or capacity. Because If I discharge at a rate of 0.6A and at 2.8V when I cut the Load, Battery voltage will definitely Increases from 2.8V to 2.9 or 3V. So is it fine or again I need to discharge till battery voltage stables at 2.8V). Also which Bit I need to observe when I stop discharge to confirm it is fully discharged.

    5) Relax for 5 Hours

    6) Start the Charging by CCCV method till the FC bit SET. (In our application we are using Charging IC to charge the battery so For charging I need to charge with that IC or I need to use standard DC source for charging which supports CCCV charging.)

    7) Relax for 2Hrs

    8) Again Dis-charge the battery same as Step 4 and Relax for 5Hrs

    9) After Step8 Update status 0 and Update status 1 both should change to 02, Right?

    Let me know if above steps are correct and also please suggest for the asked query in Steps.

    Sorry but as I am doing this first time, want to clarify all doubts to complete learning cycle perfectly.



  • Hi Madhav,

    Regarding #4, the battery needs to be discharged until the terminal voltage 2.5V. This allows for the learning cycle to properly learn the properties of the gauge, even if the application voltage is only 2.8V. 

    While doing the learning cycle, there is not a flag that goes off at terminal voltage, however this value can be confirmed by measuring the voltage of the battery. When the discharge has been stopped, this can confirmed by the DSG bit changing.

    6:The charger IC can be used for the learning cycle.

    9: Correct, Update Status should be 2.

    More information can be found in the document below: 


    Anthony Baldino