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BQ34Z100-R2: Is detection of charge termination required once learning/optimization has been performed?

Steve
Intellectual 360 points
Part Number: BQ34Z100-R2
Other Parts Discussed in Thread: BQ34Z100

Tool/software:

Hello,

In preparation for perform a learning cycle I have been reviewing the Application Report SLUA903 “Achieving The Successful Learning Cycle”  (https://www.ti.com/lit/an/slua903/slua903.pdf).  According to this document, during the portion of the learning where the pack is charged to full, the gauge must be able to successfully detect charge termination.

"At the end of charge the [FC] bit in the Flags() register should be set automatically. If it did not set then a full charge was not properly detected and the learning cycle fails."

For the purpose of the learning cycle I can use a charger that tapers the charge current at the end of charging so I should be able to supply the conditions necessary for the gauge to detect charge termination at full charge.  However, in my end application the charger we expect to use will not taper the current.  It will simply turn off the charging current once the pack voltage reaches a defined threshold.

My question is, will the gauge still function properly if used with such a charger (i.e. if it will never see the conditions necessary for it to detect charge termination)?  From what I have read about the Impedance Track algorithm I can’t tell if the algorithm uses (or requires) that capability during operation of the pack.  The pack that I am using is made up of 8 series LiFePO4 cells.

Thank you,

Steve

  • 0
    TI__Mastermind 24641 points

    Hello Steve, 

    For the IT algorithm, one of the conditions that needs to be met is the taper current must go below a certain threshold. If your charger does not have a CV phase that allows the current to taper then this could affect the gauge's ability to accurately detect a full charge (SOC=100%). 

    Regards, 

    Robert. 

  • 0 in reply to Jonny
    Intellectual 360 points

    Hi Robert,

    Thank you for responding.  That is a bit discouraging but I’m not quite ready to give up on this gauge just yet.

    From what I have read about the Impedance Tracking algorithm it seems that when the gauge detects charge termination it records the DOD as ‘DODcharge’ (or ‘DOD at EOC’ depending on the documentation).  Does the gauge record ‘DODcharge’ immediately upon determining charge termination, or does it wait until a fully relaxed state is reached?

    At some time after charge termination the gauge will detect exit from relaxation mode and when that occurs it uses the ‘DODcharge’ value to calculate a value for ‘Qstart’.  Is it correct to say that ‘Qstart’ is used to account for passed charge that has not been integrated by the gauge because in the relaxed state the current was under a specified threshold?

    Thanks again,

    Steve

  • 0 in reply to Steve
    TI__Mastermind 24641 points

    Hello Steve, 

    For specifics on the Impedance Track algorithm, I recommend referring to this document. In regards to your question about charging, please refer to the following from the BQ34Z100 TRM as this goes over the conditions that must be met in order for the gauge to detect valid charge termination (SOC = 100%). 

     

    Regards, 

    Robert.