Tracking state-of-charge during the charge phase is relatively easy with chemistries such as Li-ion where essentially none of the applied energy from the charger is lost to heat. However, lead-acid and NiMH chemistries may demonstrate significant losses to heat during charging. Therefore, to more accurately track state of charge and Time-to-Full during the charge phase, the BQ34Z100-G1 uses four charge-efficiency factors to compensate for charge acceptance. These factors are Charge Efficiency, Charge Eff Reduction Rate, Charge Effi Drop Off, and Charge Eff Temperature Compensation.

The BQ34Z100-G1 applies the Charge Efficiency when RelativeStateOfCharge() is less than the value stored in Charge Efficiency Drop Off. When RelativeStateOfCharge() is > or equal to the value coded in Charge Efficiency Drop Off, Charge Efficiency and Charge Efficiency Reduction Rate determine the charge efficiency rate. Charge Efficiency Reduction Rate defines the percent efficiency reduction per percentage point of RelativeStateOfCharge() over Charge Efficiency Drop Off. The Charge Efficiency Reduction Rate has units of 0.1%. The BQ34Z100-G1 also adjusts the efficiency factors for temperature. Charge Efficiency Temperature Compensation defines the percent efficiency reduction per degree C over 25°C. Charge Efficiency Temperature Compensation has units of 0.01%.

Applying the four factors:

Effective Charge Efficiency % = Charge Efficiency – Charge Eff Reduction Rate [RSOC() – Charge Effi Drop Off] – Charge Eff Temperature Compensation [Temperature – 25°C]

Where: RSOC() ≥ Charge Efficiency and Temperature ≥ 25°C