SLUAAT5 December 2023 BQ25756
On the EVM original RBOT of 13.7 kΩ is replaced with 30.1 kΩ which translates to VBATREG being 14.25 V. This means we can charge 14.25 V/3.6 V or about 4-cell battery. To set VBATREG more accurately which is 4x3.6 V=14.4 V, VFB_REG register is set to 1.552 V using bqStudio. The charging current is set to 2 A, pre-charge current is set to 500 mA and trickle charge current is set to 250 mA. VBAT_LOWV is set to 55% × VFB_REG and VRECHG is set to 93% × VFB_REG. The input voltage to the charger is at 31 V. With a heavily depleted battery, the charger starts charging with a trickle charge when charging is enabled by setting EN_CHG. When the battery voltage reaches pre-charge threshold, the charger employs pre-charge current. When the battery voltage is close to 7.9 V, the battery charges with full fast charge current. When the battery reaches 14.4 V the charge current is tapered down to termination current and the charging cycle is complete. Charge status register is shown as ‘charge done’. During the charging the STAT1 pin is ON and STAT2 pin is OFF indicating charge in progress. When charging is done STAT1 pin is OFF and STAT2 pin is ON.