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BQ27542 charge cycles at 4.1V

Hello,

We are planning to use the BQ27542 with our battery, but we have a question about design capacity.  We'd like to charge the battery to 4.1V to increase the battery lifetime.  We believe design capacity should initially be set to whatever corresponds to 4.2V. Once learning has been complete, we can change it to 4.1 because SOH is based off design capacity. Setting to 4.2V initially before learning will allow learning to be successful because we need 90% of passed charge of design capacity to have a successful learning.  If set it to capacity corresponding to 4.1V we might not have the 90% criteria met and learning will fail. 

So, first, is that correct?

Next, assuming that is the right approach, we are wondering how this will effect charge cycles and other parameters as the battery gets used.  How does the fuel gauge compensate for the increased life of the battery due to charging it to 4.1V?  Or, will the gauge assume the battery is being charged to 4.2V and assume the battery is bad too soon?  

Thank you,

Jamaal 

  • Hello Jamaal,

    Yes, the remarks regarding design capacity are accurate.

    If the cell is being charged to 4.1V, the Charging Voltage parameter in data flash should be set accordingly. If the Charging Voltage parameter is kept at 4.2V, the gauge might not be able to detect a primary charging termination condition. As the battery gets used, the gauge will update QMAX and RA values to reflect aging.

    Thank you.