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# BQ27510-G1

Other Parts Discussed in Thread: BQ27500

Hi,

I had a general question regarding page 15 of SLUA458, bq27500 Application Book:

"When an external load is applied, the impedance of the cell is measured by finding the difference between the measured voltage under load and the open-circuit voltage (OCV) specific to the cell chemistry at the present state-of-charge (SOC). This difference, divided by the applied load current, yields the impedance. In addition, the impedance is correlated with the temperature at time of measurement to fit in a model that accounts for temperature effects.

With the impedance information, the remaining capacity (RM) can be calculated using a voltage simulation method implemented in the firmware. The simulation starts from the present DOD, i.e., DODstart and calculates a future voltage profile under the same load with a 4% DOD increment consecutively:

V(DODI,T) = OCV (DODI,T) + I × R(DODI,T),

where DODI = DODstart + I × 4% and I represents the number of increments, and R(DODI,T) is the battery impedance under DODI and temperature T. Once the future voltage profile is calculated, the Impedance Track™ algorithm predicts the value of DOD that corresponds to the system termination voltage and captures this as DODfinal. The remaining capacity then is calculated using:

RM = (DODfinal – DODstart) × Qmax

FCC (Full-charge capacity) is the amount of charge passed from the fully charged state to the termination voltage, and can be calculated using:

FCC = Qstart + PassedCharge + RM"

By reading this, it sounds like FCC, RM, and cell impedance is calculated all from the same OCV reading.  Is this is fair assumption?

Thanks,

Anthony

• Hello Anthony,

You can assume that under normal conditions. The actual algorithm is a lot more complicated than what is printed on the application book.